Remove 'hasDns' parameter

Netd use this parameter to determine which network it should use for
DNS query when VPN is enabled. But it is no more reliable when we have
seamless vpn handover, since the parameter does not make update to
netd if we have DNS configuration change. Netd should call resolver
API to get latest DNS information rather than this one.

Bug: 116539103
Test: runtest frameworks-net passes
Change-Id: I6491114ab6de0ff66322f1da69056e6f3c999b5a