Data connection cleanup

Preliminary changes for multiple DcTracker instances, which
is part of the IWLAN refactoring work.

1. Some requests or event registrations are for cellular only, so
   added the check to make sure we don't do that on IWLAN DcTracker.
2. Removed the redundant event registration.

Test: Manual
Bug: 73659459
Change-Id: I0193ae14e7a80be9da620684639e4b2ed5ae5b0f