CTF: Play sound for enemy's flag return to base

Upon Prime's request, play a higher-pitched sound when the enemy's flag is returned to base. This is in addition to your own team's flag playing a sound when returned to base.

I think this makes sense because, in splitscreen, a sound is played no matter which team's flag is returned. In addition, the sound is not proximity-based, so design-wise I think this is OK.

Putting on next because this is technically a game-design change.

EDIT: Mystic doesn't object as long as the sounds are distinct.