This reverts commit 5e453368.

Reason for revert: Cause crash due to re-ordering the checklist while some checks are in progress

The resort of is causing inconstitency between the checks. The current uses
the list index as the ID for the STUN request. When the STUN response
(for this request) is received, the ID is used as is to retrieve the
check in the check list.
If the list is re-ordered (when receiving an new incoming check), before
the STUN response is received and processed, the ID of STUN request will
point to a different check on reception of the STUN response.

This a temporary revert until a more robust solution to the ordering
issue is found.

Change-Id: I912a9861118461ff7f6296f61c53531fa2b9384e