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_context.c

@@ -521,7 +521,8 @@ intel_glFlush(GLcontext *ctx)
     * and getting our hands on that doesn't seem worth it, so we just us the
     * first batch we emitted after the last swap.
     */
-   if (intel->first_post_swapbuffers_batch != NULL) {
+   if (!intel->using_dri2_swapbuffers &&
+       intel->first_post_swapbuffers_batch != NULL) {
       drm_intel_bo_wait_rendering(intel->first_post_swapbuffers_batch);
       drm_intel_bo_unreference(intel->first_post_swapbuffers_batch);
       intel->first_post_swapbuffers_batch = NULL;

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

@@ -186,6 +186,7 @@ struct intel_context
    struct intel_batchbuffer *batch;
    drm_intel_bo *first_post_swapbuffers_batch;
    GLboolean no_batch_wrap;
+   GLboolean using_dri2_swapbuffers;
 
    struct
    {

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;
 }