test.cmake: remove unnecessary gtest include path
test.cmake: remove unnecessary gtest include path

only googletest/include is needed for the gtest.h sub-includes.

Change-Id: Ib821a596103377c2f7a0df5f99ead209874c8ee6

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom