refactor(oohelperd): use netxlite rather than netx (#806)

The oohelperd implementation did not actually need using netx because
it was just constructing default types with logging, which is what
netxlite already does. Hence, let's avoid using netx here.

See https://github.com/ooni/probe/issues/2121

internal/cmd/oohelperd/internal/webconnectivity/measure.go

@@ -3,7 +3,6 @@ package webconnectivity
 import (
 	"context"
 	"net"
-	"net/http"
 	"net/url"
 	"sync"
 
@@ -21,7 +20,7 @@ type (
 
 // MeasureConfig contains configuration for Measure.
 type MeasureConfig struct {
-	Client            *http.Client
+	Client            model.HTTPClient
 	Dialer            model.Dialer
 	MaxAcceptableBody int64
 	Resolver          model.Resolver