Replace Context @hide APIs

Connectivity service module is using some Context @hide APIs but
they are not able to call after CS becomes a mainline module.
Thus, replace them with similar System APIs.

Bug: 170593746
Test: atest FrameworksNetTests
Test: Manully check that receiving intent and starting activity
      can work normally.
Change-Id: I0f5b53ce0da4e3fc0f927896e9a9e444048401bd