Remove superfluous base/gtest_prod_util.h includes from headers

Remove unnecessary includes. Removal mostly automated with:

git ls-files | grep '\.h$' | xargs grep -l base/gtest_prod_util.h | \
  xargs grep -L FRIEND_TEST | xargs grep -L FORWARD_DECLARE_TEST | \
  xargs ./tools/add_header.py --remove --header '"base/gtest_prod_util.h"'

Bug: 40318405
Change-Id: Ie998958f1622dd7bc6a7bfafd7dd6f737abbc909
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7240634
Reviewed-by: Mark Mentovai <mark@chromium.org>
Owners-Override: Mark Mentovai <mark@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1558386}
NOKEYCHECK=True
GitOrigin-RevId: 11f52558c4f05e1ca0f0de7dd87e413fc395d9ea