1. Stop using ConnectivityManager for VPNs in VpnDialogs.
2. Delete updateLockdownVpn, since all callers have been migrated
to calling VpnManager directly.
3. Delete the call to VpnManager in factoryReset, since the only
caller (ResetNetworkConfirm) has been updated to call into
VpnManager directly.
4. Delete getVpnManager, since it is now unused.
This reverts commit a3c05095ab.
Reason for revert: should be safe to submit now that aosp/1596096 is merged
Bug: 173331190
Test: treehugger
Change-Id: Ife3607c024006ce4fe46c981e9742170becb6331
9c0f2f10fe