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/http.go

@@ -8,6 +8,7 @@ import (
 	"sync"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/tracex"
 )
@@ -18,7 +19,7 @@ type CtrlHTTPResponse = webconnectivity.ControlHTTPRequestResult
 
 // HTTPConfig configures the HTTP check.
 type HTTPConfig struct {
-	Client            *http.Client
+	Client            model.HTTPClient
 	Headers           map[string][]string
 	MaxAcceptableBody int64
 	Out               chan CtrlHTTPResponse