core: Remove non-critical cleanup from startup aborts.

core: Remove non-critical cleanup from startup aborts.

When built-in components of Asterisk fail to start they cause the
Asterisk startup to abort.  In these cases only the most critical
cleanup should be performed - closing databases and terminating
proceses.  These cleanups are registered using ast_register_atexit, all
other cleanups should not be run during startup abort.

The main reason for this change is that these cleanup procedures are
untestable from the partially initialized states, if they fail it could
prevent us from ever running the critical cleanup with ast_run_atexits.

Change-Id: Iecc2df98008b21509925ff16740bd5fa29527db3