Revert "gdk/frameclock: add mark when we discover frames may drop"

This reverts commit 84a304e66e.

This produces marks that are confusing to me. They don't correlate
with actual gaps in the frame cycle and often overlap with regular
'window presented' marks. Also, the function we are emitting these
marks from is called from the get_frame_time getter, and we
definitely don't want to emit marks from there.

gdk/gdkframeclockidle.c

@@ -192,13 +192,6 @@ compute_smooth_frame_time (GdkFrameClock *clock,
    *        and new_frame_time >= old_frame_time. */
   frames_passed = (new_frame_time - smoothed_frame_time_base + frame_interval / 2) / frame_interval;
 
-  if (frames_passed > 1)
-    gdk_profiler_add_markf ((smoothed_frame_time_base - (frame_interval * (frames_passed-1))) * 1000L,
-                            frame_interval * (frames_passed-1) * 1000L,
-                            "Dropped Frames",
-                            "%u frames may have been dropped",
-                            frames_passed-1);
-
   /* We use an approximately whole number of frames in the future from
    * last smoothed frame time. This way we avoid minor jitter in the
    * frame times making the animation speed uneven, but still animate