Remove all non-public resolver APIs

These functions were effectively dead code since when we started hiding
all symbols in libnetd_resolv except the few that are part of the public
interface. Removing them brings us a bit closer to removing h_errno.

However, netd also calls getaddrinfo() from various places, and
currently it's taking a longer trip through bionic before landing into
android_getaddrinfofornetcontext(). This will break as soon as we change
the signature of android_getaddrinfofornetcontext(), so we should decide
what to do about this. One option would be renaming our copy of
getaddrinfo() and switch netd to it.

Test: atest netd_integration_test
Change-Id: Iacfde97203365ce4d09d8e1c1d67930d729f46b1