chan_pjsip: Remove AOR check when dialing and one is specified.

The AOR value may contain the name of an AOR or a full SIP URI.
Checking if the AOR exists can't be done as a result of this.
........

Merged revisions 428051 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@428052 f38db490-d61c-443f-a65b-d21fe96a405b