DNS Host: Removing code that was not being executed and should not be executed. (#4721)

* Removing a piece of code that was not being executed and should not be executed.

* Remove d.dns

---------

Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

features/dns/client.go

@@ -24,10 +24,6 @@ type Client interface {
 	LookupIP(domain string, option IPOption) ([]net.IP, uint32, error)
 }
 
-type HostsLookup interface {
-	LookupHosts(domain string) *net.Address
-}
-
 // ClientType returns the type of Client interface. Can be used for implementing common.HasType.
 //
 // xray:api:beta