change NMS removeNetwork to netd binder variant

Also: require NETWORK_STACK instead of CONNECTIVITY_INTERNAL.

Bug: 34953048
Bug: 64133961
Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net
Change-Id: I26f07f51a8a2f4a8bb43a276da7c5e66c355c848