net/dns/resolver: remove the Config struct.

In preparation for reintroducing a runtime reconfig Config struct.

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/userspace.go

@@ -219,11 +219,7 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
 		e.linkMonOwned = true
 	}
 
-	e.resolver = resolver.New(resolver.Config{
-		Logf:        logf,
-		Forward:     true,
-		LinkMonitor: e.linkMon,
-	})
+	e.resolver = resolver.New(logf, e.linkMon)
 
 	logf("link state: %+v", e.linkMon.InterfaceState())