race avoidance, remove MultiThreadingCriticalSection RAII instances from Lease Commands Hook library

We need to look at removing use of MultiThreadingCriticalSection instances in Lease Commands hook library command handlers. Currently all of the commands which modify leases create an instance upon entry. This means packet threads will be stopped and then recreated on every lease update, which has disconcerting implications for HA, especially in load-balancing pairs.