Remove obsolete ember-cli-terser dependency (#6312)

Apparently this dependency is no longer used when building the app with embroider

Author: Turbo87

package.json

@@ -86,7 +86,6 @@
     "ember-cli-inject-live-reload": "2.1.0",
     "ember-cli-mirage": "2.4.0",
     "ember-cli-notifications": "8.0.0",
-    "ember-cli-terser": "4.0.2",
     "ember-click-outside": "6.0.1",
     "ember-concurrency": "3.0.0",
     "ember-css-modules": "2.0.1",