Revert "res_pjsip_outbound_registration.c: Use our own scheduler and other stuff"

This reverts commit 860e40dd.

Reason for revert: Too many issues reported.  Need to research and correct.

ASTERISK-29230
ASTERISK-29231
Reported by: Michael Maier

Change-Id: I9011e2eecda4e91e1cfeeda6d1a7f1a0453eab41