Remove GtestMatchers and GtestMatchersTest (llvm#162524)

Fixes issue llvm#161939.
This PR removes the unused GtestMatchers and GtestMatchersTest.

Author: Thibault-Monnier

clang/include/clang/ASTMatchers/GtestMatchers.h

@@ -8,7 +8,6 @@ set(LLVM_LINK_COMPONENTS
 add_clang_library(clangASTMatchers
   ASTMatchFinder.cpp
   ASTMatchersInternal.cpp
-  GtestMatchers.cpp
   LowLevelHelpers.cpp
 
   LINK_LIBS

clang/lib/ASTMatchers/CMakeLists.txt

@@ -3,7 +3,6 @@ add_clang_unittest(ASTMatchersTests
   ASTMatchersNodeTest.cpp
   ASTMatchersNarrowingTest.cpp
   ASTMatchersTraversalTest.cpp
-  GtestMatchersTest.cpp
   CLANG_LIBS
   clangAST
   clangASTMatchers