Revert "OpenGL core: add some missing gpuBegin to allow clay with no UI"

This reverts commit 1c01811cce.

It broke everything.

source/blender/editors/screen/area.c

@@ -451,7 +451,6 @@ static void region_draw_azones(ScrArea *sa, ARegion *ar)
 	glEnable(GL_BLEND);
 	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
-	gpuMatrixBegin2D();
 	gpuPushMatrix();
 	gpuTranslate2f(-ar->winrct.xmin, -ar->winrct.ymin);
 	

source/blender/windowmanager/intern/wm_subwindow.c

@@ -338,7 +338,6 @@ void wmOrtho2(float x1, float x2, float y1, float y2)
 	if (x1 == x2) x2 += 1.0f;
 	if (y1 == y2) y2 += 1.0f;
 
-	gpuMatrixBegin3D();
 	gpuOrtho(x1, x2, y1, y2, -100, 100);
 }