Instead of using a separate service-mdns library, move the code to
service-connectivity-t.
service-connectivity-t is chosen because it has access to hidden API of
classes that were made updatable in T, such as NsdServiceInfo and
NsdManager. mdns code can be there as it is only loaded on T+.
Bug: 241738458
Test: atest
Change-Id: I7eb6c9ab8bf0e0a614ea2994c6ed80a1a780241f