Mark more BUILD_* as obsolete

These have been warnings for a couple weeks now, with no hits.

  BUILD_AUX_EXECUTABLE
  BUILD_AUX_STATIC_LIBRARY
  BUILD_HOST_FUZZ_TEST
  BUILD_HOST_NATIVE_TEST
  BUILD_HOST_STATIC_TEST_LIBRARY
  BUILD_NATIVE_BENCHMARK
  BUILD_STATIC_TEST_LIBRARY

Fixes: 130735607
Fixes: 130735003
Fixes: 130691889
Fixes: 130723134
Fixes: 130722660
Fixes: 130734558
Fixes: 130735594
Test: check all downstream build_test logs
Change-Id: Ia13e59200af8f77a79d6a17d94913b79d8970055