Remove __SYCL_DISABLE_NAMESPACE_INLINE__ support

This PR breaks it, but it doesn't matter because next PR would remove
cl:: completely.

Author: aelovikov-intel

sycl/include/sycl/detail/defines_elementary.hpp

@@ -8,11 +8,9 @@
 
 #pragma once
 
-#ifndef __SYCL_DISABLE_NAMESPACE_INLINE__
 #define __SYCL_INLINE_NAMESPACE(X) inline namespace X
-#else
-#define __SYCL_INLINE_NAMESPACE(X) namespace X
-#endif // __SYCL_DISABLE_NAMESPACE_INLINE__
+
+#define __SYCL_INLINE_VER_NAMESPACE(X) inline namespace X
 
 #ifndef __has_attribute
 #define __has_attribute(x) 0