Remove stale comment about glFlush().

We don't need an MI_FLUSH there, because everything that's been flushed in the
batch will eventually hit the hardware.

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

@@ -361,9 +361,6 @@ intelFlush(GLcontext * ctx)
 
    if (intel->batch->map != intel->batch->ptr)
       intel_batchbuffer_flush(intel->batch);
-
-   /* XXX: Need to do an MI_FLUSH here.
-    */
 }
 
 void