Reset VPN settings by calling VpnManager.

Currently, ConnectivityManager#factoryReset calls
VpnManager#factoryReset. Call the VpnManager method directly so
it can be removed from ConnectivityManager.

Bug: 173331190
Test: atest SettingsRoboTests
Change-Id: I7c702a627cd448dbde40e0d885fbc570ecd1e55d
1 file changed