[SYCL][NFC] Drop suppression of export related warnings (#17918)

Right now it's applied globally, affecting code other than SYCL headers
when included. After removing the pragma, no additional warnings are
observed when building on Windows.

Author: sergey-semenov

sycl/include/sycl/detail/export.hpp

@@ -12,11 +12,6 @@
 #ifndef __SYCL_EXPORT
 #ifdef _WIN32
 
-// MSVC discourages export of classes, that use STL class in API. This
-// results in a warning, treated as compile error. Silence C4251 to workaround.
-#pragma warning(disable : 4251)
-#pragma warning(disable : 4275)
-
 #define __SYCL_DLL_LOCAL
 
 #if __SYCL_BUILD_SYCL_DLL