Restrict visibility of absl/container:hash_function_defaults.

PiperOrigin-RevId: 496514638
Change-Id: I45b8dfe01c83915c460711339d2d8c38604c8d81

Author: ckennelly

Diff for: absl/container/BUILD.bazel

@@ -393,6 +393,9 @@ cc_library(
     hdrs = ["internal/hash_function_defaults.h"],
     copts = ABSL_DEFAULT_COPTS,
     linkopts = ABSL_DEFAULT_LINKOPTS,
+    visibility = [
+        "//visibility:private",
+    ],
     deps = [
         "//absl/base:config",
         "//absl/hash",