Do not force -O2 flag in hardening-enabled builds

Author: mshabunin

cmake/OpenCVCompilerDefenses.cmake

@@ -87,11 +87,3 @@ endif()
 set( CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${OPENCV_LINKER_DEFENSES_FLAGS_COMMON}" )
 set( CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} ${OPENCV_LINKER_DEFENSES_FLAGS_COMMON}" )
 set( CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OPENCV_LINKER_DEFENSES_FLAGS_COMMON}" )
-
-if(CV_GCC OR CV_CLANG)
-  foreach(flags
-          CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG
-          CMAKE_C_FLAGS CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_DEBUG)
-    string(REPLACE "-O3" "-O2" ${flags} "${${flags}}")
-  endforeach()
-endif()