cleanup(netx): remove subpackages and unnecessary code (#788)

This pull request consists of several small and obvious cleanups in the netx directory.

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

internal/engine/netx/httptransport.go

@@ -0,0 +1,38 @@
+package netx
+
+import (
+	"crypto/tls"
+
+	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
+)
+
+// httpTransportConfig contains the configuration required for constructing an HTTP transport
+type httpTransportConfig struct {
+	Dialer     model.Dialer
+	QUICDialer model.QUICDialer
+	TLSDialer  model.TLSDialer
+	TLSConfig  *tls.Config
+}
+
+// newHTTP3Transport creates a new HTTP3Transport instance.
+//
+// Deprecation warning
+//
+// New code should use netxlite.NewHTTP3Transport instead.
+func newHTTP3Transport(config httpTransportConfig) model.HTTPTransport {
+	// Rationale for using NoLogger here: previously this code did
+	// not use a logger as well, so it's fine to keep it as is.
+	return netxlite.NewHTTP3Transport(model.DiscardLogger,
+		config.QUICDialer, config.TLSConfig)
+}
+
+// newSystemTransport creates a new "system" HTTP transport. That is a transport
+// using the Go standard library with custom dialer and TLS dialer.
+//
+// Deprecation warning
+//
+// New code should use netxlite.NewHTTPTransport instead.
+func newSystemTransport(config httpTransportConfig) model.HTTPTransport {
+	return netxlite.NewOOHTTPBaseTransport(config.Dialer, config.TLSDialer)
+}