Remove ConnectivityManager swapActiveStatsMap API

swapActiveStatsMap is temporary added for the NetworkStatsFactory to
call BpfNetMaps#swapActiveStatsMap in tethering mainline module. Now
NetworkStatsFactory already be mainlined, calling BpfNetMaps#swapActiveStatsMap
directly.

Bug: 218494448
Test: atest ConnectivityCoverageTests
      atest FrameworksNetTests
Change-Id: I25618020c078c7de3f0036c48d06d7816a431f62