Modify Telecom to have "one call ID to rule them all".

- Add call ID to the Telecom call class.
- Modify CallIdMapper to use Telecom call ID instead of a new sequentially
generated one.
- Remove isValidCallId and isValidConferenceId from CallIdMapper as they
are no longer required.
- Modify event logger to use telecom call ID instead of a sequential ID.

Bug: 23357902
Change-Id: I485f751d1668e96b7787c4be97aa76c1e5ec0798