Reverts #34133.

To quote #34474 (comment):

Previously:

 0:19.03 TEST_START: /css/cssom-view/scroll-behavior-smooth-navigation.html
 0:37.04 INFO Got timeout in harness
 0:37.04 DEBUG Got command: 'test_ended'
 0:37.04 DEBUG Unexpected count in this thread 1
 0:37.04 TEST_END: TIMEOUT, expected ERROR - TestRunner hit external timeout (this may indicate a hang)
 0:37.04 DEBUG new state: restarting
 0:37.04 DEBUG Dispatch restart_runner
 0:37.04 DEBUG Stopping WebDriver
 0:37.07 DEBUG OutputHandler.after_process_stop
 0:37.07 DEBUG Going to stop Safari
 0:37.14 DEBUG Stopping Safari 46683
 0:37.17 DEBUG ensure_runner_stopped
 0:37.17 DEBUG Stopping WebDriver
 0:37.17 DEBUG Going to stop Safari
 0:37.23 DEBUG waiting for runner process to end
 0:37.23 DEBUG After join
 0:37.23 DEBUG Runner process exited with code 0
 0:37.23 DEBUG TestRunnerManager cleanup
 0:37.06 WARNING Traceback (most recent call last):
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/wptrunner/wptrunner/executors/base.py", line 301, in run_test
    result = self.do_test(test)
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 459, in do_test
    success, data = WebDriverRun(self.logger,
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/wptrunner/wptrunner/executors/base.py", line 205, in run
    if self.protocol.is_alive():
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 385, in is_alive
    self.webdriver.send_session_command("GET", "window", timeout=2)
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/webdriver/webdriver/client.py", line 661, in send_session_command
    return self.send_command(method, url, body, timeout)
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/webdriver/webdriver/client.py", line 613, in send_command
    response = self.transport.send(
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/webdriver/webdriver/transport.py", line 234, in send
    response = self._request(method, uri, payload, headers, timeout=None)
  File "/Volumes/gsnedders/projects/wpt/web-platform-tests/tools/webdriver/webdriver/transport.py", line 259, in _request
    response = self.connection.getresponse()
  File "Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 1349, in getresponse
    response.begin()
  File "Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 316, in begin
    version, status, reason = self._read_status()
  File "Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 285, in _read_status
    raise RemoteDisconnected("Remote end closed connection without"
http.client.RemoteDisconnected: Remote end closed connection without response

 0:37.23 WARNING Command left in command_queue during cleanup: 'test_ended', (<wptrunner.wpttest.TestharnessTest /css/cssom-view/scroll-behavior-smooth-navigation.html>, (<wptrunner.wpttest.TestharnessResult INTERNAL-ERROR>, []))
 0:37.06 DEBUG Hanging up on WebDriver session
 0:37.06 INFO Closing logging queue
 0:37.06 INFO queue closed
 0:37.23 DEBUG new state: initializing
 0:37.23 DEBUG Dispatch init
 0:37.23 DEBUG Init called, starting browser and runner
 0:37.23 DEBUG Starting browser with settings {}
 0:37.23 DEBUG Starting WebDriver: /Applications/Safari Technology Preview.app/Contents/MacOS/safaridriver --port=58923
 0:37.24 DEBUG OutputHandler.after_process_start
 0:37.24 DEBUG Trying to connect to 127.0.0.1:58923
 0:37.74 DEBUG Connected to 127.0.0.1:58923
 0:37.74 DEBUG OutputHandler.start
 0:37.74 DEBUG _run complete
 0:37.74 INFO Starting runner
 0:37.75 DEBUG Test runner started
 0:38.96 DEBUG Got command: 'log'
 0:38.95 DEBUG Executor setup
 0:38.96 DEBUG Got command: 'log'
 0:38.95 DEBUG Connecting to WebDriver on URL: http://127.0.0.1:58923/
 0:40.26 DEBUG Got command: 'log'
 0:40.26 DEBUG Loading http://web-platform.test:8000/testharness_runner.html
 0:40.34 DEBUG Got command: 'init_succeeded'
 0:40.34 DEBUG new state: running
 0:40.34 DEBUG Dispatch run_test
 0:40.34 TEST_START: /css/cssom-view/window-screen-width.html
 0:40.34 DEBUG Got command: 'log'
 0:40.34 DEBUG Executor setup done
 0:40.63 DEBUG Got command: 'log'
 0:40.63 DEBUG Got async callback: complete
 0:40.71 DEBUG Got command: 'test_ended'
 0:40.71 TEST_END: Test OK. Subtests passed 3/3. Unexpected 0

After 62c3bc7 (#34133):

 0:31.30 TEST_START: /css/cssom-view/scroll-behavior-smooth-navigation.html
0:49.30 INFO Got timeout in harness
0:49.30 DEBUG Got command: 'test_ended'
0:49.30 DEBUG Unexpected count in this thread 1
0:49.30 TEST_END: TIMEOUT, expected ERROR - TestRunner hit external timeout (this may indicate a hang)
0:49.30 DEBUG new state: running
0:49.30 DEBUG Dispatch run_test
0:49.30 TEST_START: /css/cssom-view/window-screen-width.html
1:04.80 INFO Got timeout in harness
1:04.80 DEBUG Got command: 'test_ended'
1:04.80 DEBUG Unexpected count in this thread 2
1:04.80 TEST_END: TIMEOUT, expected OK - TestRunner hit external timeout (this may indicate a hang)

Thus we see a change in behaviour with external timeouts following #34133, reverting that.

I'm not sure what's wrong with the change in #34133, but this is completely reproducible locally when the test times out.