Clean up Netd and libnetd_resolv for resolver related commands

1. remove all resolver related commands in netd
2. remove unused API in libnetd_resolv

Bug: 126141549
Test: built, flashed, booted
      system/netd/tests/runtests.sh pass

Change-Id: I35ac8f241eebd6284a6a685ef86cd77a1fce4388