player: don't block playback stop when seeking

This was added for A-B loops, but it looks like commit a1dec6f5 made
this code unnecessary. Remove it, because it has the annoying
side-effect of blocking playback stop when seeking past the end.

player/playloop.c

@@ -1109,9 +1109,6 @@ void run_playloop(struct MPContext *mpctx)
 
     handle_sstep(mpctx);
 
-    if (mpctx->stop_play == AT_END_OF_FILE && mpctx->seek.type)
-        mpctx->stop_play = KEEP_PLAYING;
-
     if (mpctx->stop_play)
         return;