Drop dead code in sun.net

This covers the following unused classes:
 - InetAddressCachePolicy
 - RegisteredDomain
 - TransferProtocolClient

This CL doesn't cover sub-packages; these are covered by
different CLs / child-bugs.

Bug: 34799240
Test: make cts droid checkbuild
Test: device still boots after flashing
Test: CtsLibcoreTestCases
Test: Performed a quick search to verify that at least parts of
      all other classes that are directly in sun.net are used
      somewhere.
Change-Id: I0019a321a1934f9d940217132648568a13e301ca