OpenGL: remove some hacks/workarounds

Everything I've tested works fine without these hacks. Variety of Mac, Linux, Windows, Intel, nVidia, AMD.
If these workarounds are for old unsupported systems let's clean house.

Reviewers: #opengl_gfx

Differential Revision: https://developer.blender.org/D1707

source/blender/editors/include/BIF_glutil.h

@@ -185,8 +185,6 @@ void gla2DGetMap(gla2DDrawInfo *di, struct rctf *rect);
 void gla2DSetMap(gla2DDrawInfo *di, struct rctf *rect);
 #endif
 
-/* intel gfx cards frontbuffer problem */
-// void bglFlush(void); /* UNUSED */
 void set_inverted_drawing(int enable);
 void setlinestyle(int nr);
 

source/blender/editors/screen/glutil.c

@@ -814,17 +814,6 @@ void bglPolygonOffset(float viewdist, float dist)
 	}
 }
 
-#if 0 /* UNUSED */
-void bglFlush(void) 
-{
-	glFlush();
-#ifdef __APPLE__
-//	if (GPU_type_matches(GPU_DEVICE_INTEL, GPU_OS_MAC, GPU_DRIVER_OFFICIAL))
-// XXX		myswapbuffers(); //hack to get mac intel graphics to show frontbuffer
-#endif
-}
-#endif
-
 /* **** Color management helper functions for GLSL display/transform ***** */
 
 /* Draw given image buffer on a screen using GLSL for display transform */