GPUCompositing: Remove entire module.

This module has no use now with the new DrawManager and DrawEngines and it
is using deprecated paths.

Moving gpu_shader_fullscreen_vert.glsl
to draw/modes/shaders/common_fullscreen_vert.glsl

source/blender/python/intern/gpu_offscreen.c

@@ -37,7 +37,6 @@
 
 #include "ED_screen.h"
 
-#include "GPU_compositing.h"
 #include "GPU_framebuffer.h"
 #include "GPU_texture.h"