utils.h: Deprecate `ast_gethostbyname()`. (#79)

utils.h: Deprecate `ast_gethostbyname()`. (#79)

Deprecate `ast_gethostbyname()` in favor of `ast_sockaddr_resolve()` and
`ast_sockaddr_resolve_first_af()`. `ast_gethostbyname()` has not been
used by any in-tree code since 2021.

This function will be removed entirely in Asterisk 23.

Resolves: #78

UpgradeNote: ast_gethostbyname() has been deprecated and will be removed
in Asterisk 23. New code should use `ast_sockaddr_resolve()` and
`ast_sockaddr_resolve_first_af()`.