change CS_DONE to CS_DESTROY and add state handler for destroy and tear down critical parts of the channel from this method which is not called until it's impossible for anything to be referencing the channel (after final write lock and before destroying the pool)

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@12986 d0543943-73ff-0310-b7d9-9358b9ac24b2