Revert "opengl: drop less frames when clip and display have similar fps"

This reverts commit f1746741de.

Together with the other revert, this fixes #2023 (the reason being
broken framedrop handling - it was dropping frames when it shouldn't).

video/out/vo.c

@@ -626,15 +626,7 @@ static bool render_frame(struct vo *vo)
     if (!in->hasframe_rendered)
         duration = -1; // disable framedrop
 
-    // if the clip and display have similar/identical fps, it's possible that
-    // we'll be very slightly late frequently due to timing jitter, or if the
-    // clip/container timestamps are not very accurate.
-    // so if we dropped the previous frame, keep dropping until we're aligned
-    // perfectly, else, allow some slack (1 vsync) to let it settle into a rhythm.
-    in->dropped_frame = duration >= 0 &&
-                            ((in->dropped_frame && end_time < next_vsync) ||
-                            (end_time < prev_vsync)); // hard threshold - 1 vsync late
-
+    in->dropped_frame = duration >= 0 && end_time < next_vsync;
     in->dropped_frame &= !(vo->driver->caps & VO_CAP_FRAMEDROP);
     in->dropped_frame &= (vo->global->opts->frame_dropping & 1);
     // Even if we're hopelessly behind, rather degrade to 10 FPS playback,