Clear process DNS NetID binding when expiring or releaseing legacy requests.

When requests made by ConnectivityManager.startUsingNetworkFeature() are
expired or are canceled via ConnectivityManager.stopUsingNetworkFeature(),
we must remember to clear the binding of DNS requests from the calling
process to the Network satisfying the request.

bug:18778725
Change-Id: I800c808ac6486000241b5d263aa79a1192a9fe9e