cleanup: use NewHTTPTransportWithResolver more often (#808)

We can simplify code in a bunch of places using a useful factory.

Part of https://github.com/ooni/probe/issues/2121.

internal/engine/geolocate/iplookup.go

@@ -86,10 +86,7 @@ func (c ipLookupClient) doWithCustomFunc(
 	// Implementation note: we MUST use an HTTP client that we're
 	// sure IS NOT using any proxy. To this end, we construct a
 	// client ourself that we know is not proxied.
-	dialer := netxlite.NewDialerWithResolver(c.Logger, c.Resolver)
-	handshaker := netxlite.NewTLSHandshakerStdlib(c.Logger)
-	tlsDialer := netxlite.NewTLSDialer(dialer, handshaker)
-	txp := netxlite.NewHTTPTransport(c.Logger, dialer, tlsDialer)
+	txp := netxlite.NewHTTPTransportWithResolver(c.Logger, c.Resolver)
 	clnt := &http.Client{Transport: txp}
 	defer clnt.CloseIdleConnections()
 	ip, err := fn(ctx, clnt, c.Logger, c.UserAgent)