health 2.0 VTS: require GTEST_SKIP to be defined

This is a hack to support the test in Android P. Now that gtest
has been updated, we no longer need this hack.

Test: run it
Bug: 118852225
Bug: 136717180
Change-Id: I81802b6fae0dc7839aa9fd1dd40cb881ff4eefdb
(cherry picked from commit 9fb96fa4)
Merged-In: I81802b6fae0dc7839aa9fd1dd40cb881ff4eefdb