Simplify the server freeing TX mechanism
Simplify the server freeing TX mechanism

A transaction handler doesn't need to send `free` message to inform
server about deleting because the server can do it by `EXIT` message
which will be sent when the transaction is finished.

Also, instead of ets:match_delete/2 use ets:delete/2 and ets:take/2
and additional insert with {HandlerPid, ReqKey}

surik/eradius