video_core/const_buffer_locker: Remove #pragma once from cpp file

Silences a compiler warning.

src/video_core/shader/const_buffer_locker.cpp

@@ -2,8 +2,6 @@
 // Licensed under GPLv2 or any later version
 // Refer to the license.txt file included.
 
-#pragma once
-
 #include <algorithm>
 #include <memory>
 #include "common/assert.h"