intel: Remove dead intel_drawbuf_region().

Since the glBitmap() MRT change, it's unused.  There was basically no way
to responsibly use this function since MRT was introduced.

Reviewed-and-tested-by: Ian Romanick <ian.d.romanick@intel.com>
Acked-by: Paul Berry <stereotype441@gmail.com>

src/mesa/drivers/dri/intel/intel_buffers.c

@@ -34,20 +34,6 @@
 #include "main/framebuffer.h"
 #include "main/renderbuffer.h"
 
-/**
- * Return pointer to current color drawing region, or NULL.
- */
-struct intel_region *
-intel_drawbuf_region(struct intel_context *intel)
-{
-   struct intel_renderbuffer *irbColor =
-      intel_renderbuffer(intel->ctx.DrawBuffer->_ColorDrawBuffers[0]);
-   if (irbColor && irbColor->mt)
-      return irbColor->mt->region;
-   else
-      return NULL;
-}
-
 /**
  * Return pointer to current color reading region, or NULL.
  */

src/mesa/drivers/dri/intel/intel_buffers.h

@@ -38,8 +38,6 @@ struct intel_framebuffer;
 
 extern struct intel_region *intel_readbuf_region(struct intel_context *intel);
 
-extern struct intel_region *intel_drawbuf_region(struct intel_context *intel);
-
 extern void intel_check_front_buffer_rendering(struct intel_context *intel);
 
 static inline void