[CMake] Remove unnecessary cmake_{push,pop}_check_state() pair

cmake/modules/CheckCXXFeatures.cmake

@@ -27,7 +27,6 @@
 
 
 include(CMakePushCheckState)
-cmake_push_check_state()
 
 # test for C++14 flags
 if(NOT DISABLE_CXX_VERSION_CHECK)
@@ -230,8 +229,6 @@ check_cxx_source_compiles("
   )
 
 
-cmake_pop_check_state()
-
 # find the threading library
 # Use a copy FindThreads from CMake 3.1 due to its support of pthread
 if(NOT DEFINED THREADS_PREFER_PTHREAD_FLAG)