[SYCL][USM][NFC] Remove unnecessary includes from usm_impl.hpp. (#1823)

Signed-off-by: James Brodman <[email protected]>

Author: jbrodman

sycl/include/CL/sycl/detail/usm_impl.hpp

@@ -7,8 +7,6 @@
 // ===--------------------------------------------------------------------=== //
 #pragma once
 
-#include <CL/cl_usm_ext.h>
-#include <CL/sycl/detail/cl.h>
 #include <CL/sycl/detail/export.hpp>
 #include <CL/sycl/usm/usm_enums.hpp>