Do not include internal GTest header.

Only the headers gtest.h and gtest-spi.h are public.  This
inclusion is causing a build break when upgrading googletest
to version 1.13.0.

Bug: 271622675
Test: local build, presubmit
Change-Id: I698e4d4464c131e9dad73a23a6f65908a07e9f60