Cleaned up dead code

Cleaned up dead code for CleanupDataConnection and
CleanupAllDataConnections. Also renamed the internal
version.

There is no logic change in this change.

Test: Unit tests and telephony sanity tests
Bug: 73659459
Merged-In: I3c9ed9502960c3f743f41078089cfff611cd96b0
Change-Id: I3c9ed9502960c3f743f41078089cfff611cd96b0
(cherry picked from commit 746d1044)