[SPARK-4756][SQL] FIX: sessionToActivePool grow infinitely, even as sessions expire

**sessionToActivePool** in **SparkSQLOperationManager** grow infinitely, even as sessions expire.
we should remove the pool value when the session closed, even though **sessionToActivePool** would not exist in all of sessions.

Author: guowei2 <guowei2@asiainfo.com>

Closes #3617 from guowei2/SPARK-4756 and squashes the following commits:

e9b97b8 [guowei2] fix compile bug with Shim12
cf0f521 [guowei2] Merge remote-tracking branch 'apache/master' into SPARK-4756
e070998 [guowei2] fix: remove active pool of the session when it expired