IMS/911: Do not clear handover connections on SRVCC COMPLETE

Even though SRVCC or silent redial is successful, the handover connection
objects are cleared before migrated to CS domain. Proper checks are added
NOT to clear the handover connection objects as they are removed as and
when a new driver call via CS pipe is received and processed.

Change-Id: I061fa81e651b4c6b6bdea1f1cf0b09dde39fdb4a
CRs-Fixed: 713730