sla: remove redundant locking.

sla.lock was already locked in the only place that sla_check_reload() was called.
Remove the redundant locking of sla.lock done in this function.  Less recursive
locking is A Good Thing.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@386190 f38db490-d61c-443f-a65b-d21fe96a405b