Remove Mac-specific DNSServiceRef resolver

[djs55]

This code hasn't been used for a long time. Let's remove it to remove the dependency.

The plan is to:

• remove unused code
• remove unnecessary dependencies

and then it will be much easier to

• update the remaining dependencies
• modernise the code
• fix long-standing bugs
• improve performance

Signed-off-by: David Scott dave@recoil.org