chan_pjsip: Revert r403587

This patch was intended to eliminate a deadlock that occurs when
masquerades occur in pjsip channels, but has some potential side
effects. Mark Michelson is currently working on addressing this
problem from another angle.

(issue ASTERISK-22936)
Reported by: Jonathan Rose
........

Merged revisions 403705 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403707 65c4cc65-6c06-0410-ace0-fbb531ad65f3