cleanup: netx does not use netxlite legacy names (#801)

This diff refactors netx and netxlite to ensure we're not using
netxlite legacy names inside of netx.

To this end, we're cheating a bit. We're exposing a new factory to
get an unwrapped stdlib resolver rather than defining a legacy name
to export the private name of the same factory.

This is actually a fine place to stop, for now, the next and
netxlite refactoring at https://github.com/ooni/probe/issues/2121.

internal/engine/geolocate/geolocate.go

@@ -114,7 +114,7 @@ func NewTask(config Config) *Task {
 		config.UserAgent = fmt.Sprintf("ooniprobe-engine/%s", version.Version)
 	}
 	if config.Resolver == nil {
-		config.Resolver = netxlite.NewResolverStdlib(config.Logger)
+		config.Resolver = netxlite.NewStdlibResolver(config.Logger)
 	}
 	return &Task{
 		countryLookupper:     mmdbLookupper{},