Drop custom gtest configuration

We currently hardcode gtest include directories in a few places. This doesn't seem to be necessary, and should be taken care of by gtest itself at https://github.com/google/googletest/blob/e588eb1ff9ff6598666279b737b27f983156ad85/googletest/CMakeLists.txt#L118

Related to #951

Closes https://github.com/google/iree/pull/954

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/iree/pull/954 from GMNGeoffrey:test-drop-custom-gtest b7d34015cae944e56a3ed81c83596d6ef6bdcac7
PiperOrigin-RevId: 298951691

build_tools/cmake/iree_cc_binary.cmake

diff --git a/build_tools/cmake/iree_cc_binary.cmake b/build_tools/cmake/iree_cc_binary.cmake
index 1afea94..5b9320d 100644
--- a/build_tools/cmake/iree_cc_binary.cmake
+++ b/build_tools/cmake/iree_cc_binary.cmake
@@ -91,8 +91,6 @@
     target_include_directories(${_NAME}
       PUBLIC
         ${IREE_COMMON_INCLUDE_DIRS}
-      PRIVATE
-        ${GTEST_INCLUDE_DIRS}
     )
     target_compile_definitions(${_NAME}
       PUBLIC

build_tools/cmake/iree_cc_test.cmake

diff --git a/build_tools/cmake/iree_cc_test.cmake b/build_tools/cmake/iree_cc_test.cmake
index eeaf651..bc59707 100644
--- a/build_tools/cmake/iree_cc_test.cmake
+++ b/build_tools/cmake/iree_cc_test.cmake
@@ -79,8 +79,6 @@
   target_include_directories(${_NAME}
     PUBLIC
       ${IREE_COMMON_INCLUDE_DIRS}
-    PRIVATE
-      ${GTEST_INCLUDE_DIRS}
   )
   target_compile_definitions(${_NAME}
     PUBLIC

build_tools/cmake/iree_copts.cmake

diff --git a/build_tools/cmake/iree_copts.cmake b/build_tools/cmake/iree_copts.cmake
index c08c462..3ef833e 100644
--- a/build_tools/cmake/iree_copts.cmake
+++ b/build_tools/cmake/iree_copts.cmake
@@ -111,10 +111,6 @@
 #-------------------------------------------------------------------------------
 
 set(INSTALL_GTEST OFF CACHE BOOL "" FORCE)
-set(GTEST_INCLUDE_DIRS
-  "${CMAKE_CURRENT_SOURCE_DIR}/third_party/googletest/include/"
-  "${CMAKE_CURRENT_SOURCE_DIR}/third_party/googlemock/include/"
-)
 set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 
 #-------------------------------------------------------------------------------