Remove legacy remote authentication code in Bazel mode

Atest no longer requires authentication scripts now that Bazel supports
credential helpers.

See
https://bazel.build/reference/command-line-reference#flag--experimental_credential_helper for more details.

Bug: 254607314
Test: atest --host atest_unittests
Change-Id: Ica4026109abd1cb73c784e31e6c8abb965888d27
1 file changed