[IT05] Remove the unused network activity logic out from NMS

The network activity logic is moved to ConnectivityService.
CS is no longer setting the idle timer via NMS to netd. The
idle timer should only set from CS, so remove the network
activity logic out from NMS.

Bug: 170598012
Test: atest FrameworksNetTests
Change-Id: Ief9e892586aaee8e9542b9313088fa50d1d411e5
2 files changed