intel: Don't do client-side frame throttling with DRI2 SwapBuffers.

The server side does the throttling on our behalf now by putting the
client to sleep, so we don't need our previous hacks for limiting the
number of outstanding frames.  Same effect as
7d4e674b21.

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

@@ -126,6 +126,10 @@ intelDRI2Flush(__DRIdrawable *drawable)
 static void
 intelDRI2FlushInvalidate(__DRIdrawable *drawable)
 {
+   struct intel_context *intel = drawable->driContextPriv->driverPrivate;
+
+   intel->using_dri2_swapbuffers = GL_TRUE;
+
    intelDRI2Flush(drawable);
    drawable->validBuffers = GL_FALSE;
 }