Removed stray apostrophe.

Apparently the pluralization of an acronym does not use an apostophe,
according to most modern style guides. I feel like I've been living a
lie this whole time.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@393100 f38db490-d61c-443f-a65b-d21fe96a405b