cmake: fix C++11 flags (ENABLE_CXX11 is not required)

cmake/OpenCVDetectCXXCompiler.cmake

@@ -176,7 +176,7 @@ if(CMAKE_CXX11_COMPILE_FEATURES)
 endif()
 if(NOT HAVE_CXX11)
   ocv_check_compiler_flag(CXX "" HAVE_CXX11 "${OpenCV_SOURCE_DIR}/cmake/checks/cxx11.cpp")
-  if(NOT HAVE_CXX11 AND ENABLE_CXX11)
+  if(NOT HAVE_CXX11)
     ocv_check_compiler_flag(CXX "-std=c++11" HAVE_STD_CXX11 "${OpenCV_SOURCE_DIR}/cmake/checks/cxx11.cpp")
     if(HAVE_STD_CXX11)
       set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

cmake/OpenCVDetectInferenceEngine.cmake

@@ -17,13 +17,6 @@
 # INF_ENGINE_TARGET - set to name of imported library target representing InferenceEngine
 #
 
-if(NOT HAVE_CXX11)
-    message(WARNING "DL Inference engine requires C++11. You can turn it on via ENABLE_CXX11=ON CMake flag.")
-    return()
-endif()
-
-# =======================
-
 function(add_custom_ie_build _inc _lib _lib_rel _lib_dbg _msg)
   if(NOT _inc OR NOT (_lib OR _lib_rel OR _lib_dbg))
     return()