res_musiconhold: Minor cleanup.

Fix a few free()'s that should be ast_free()'s. Reverted an old
workaround that isn't necessary. Reorder a tiny bit of code.
Remove a bit of commented-out code.

Review: https://reviewboard.asterisk.org/r/3536/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@413894 f38db490-d61c-443f-a65b-d21fe96a405b