Remove Vpn#isBlockingUid.

This code is no longer used. Delete it and the tests for it.

One of the tests checks that when a restricted profile is added,
the lockdown UID rules are updated to cover that profile as well.
ConnectivityServiceTest does not currently has coverage for this,
so add it.

Bug: 173331190
Test: moved unit test from VpnTest to ConnectivityServiceTest
Change-Id: Ic350b90946870890bf031668bb5c201037b0bd15