mythburn.py: fix playback problem with some players

* Remove the redundant pause="0" attributes they aren't required.
* Remove the pause="inf" from the menus they loop forever so the pause is
  redundant.

I wasn't able to reproduce the problems in the ticket but should fix #9703.

(cherry picked from commit a8f37289c61e86e771ae10f73a3fad713e21cea6)