refactor: only use shaping dialer for ndt7 and dash (#754)

See https://github.com/ooni/probe/issues/2112 for context.

While there, run `go fix -fix buildtag ./...`

internal/netxlite/shaping_shaping_test.go

@@ -0,0 +1,66 @@
+//go:build shaping
+
+package netxlite
+
+import (
+	"context"
+	"errors"
+	"net"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/model/mocks"
+)
+
+func TestNewShapingDialerx(t *testing.T) {
+	t.Run("failure", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		d := &mocks.Dialer{
+			MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
+				return nil, expected
+			},
+		}
+		shd := NewMaybeShapingDialer(d)
+		conn, err := shd.DialContext(context.Background(), "tcp", "8.8.8.8:443")
+		if !errors.Is(err, expected) {
+			t.Fatal("unexpected err", err)
+		}
+		if conn != nil {
+			t.Fatal("expected nil conn")
+		}
+	})
+
+	t.Run("success", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		uc := &mocks.Conn{
+			MockRead: func(b []byte) (int, error) {
+				return 0, expected
+			},
+			MockWrite: func(b []byte) (int, error) {
+				return 0, expected
+			},
+		}
+		d := &mocks.Dialer{
+			MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
+				return uc, nil
+			},
+		}
+		shd := NewMaybeShapingDialer(d)
+		conn, err := shd.DialContext(context.Background(), "tcp", "8.8.8.8:443")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, ok := conn.(*shapingConn); !ok {
+			t.Fatal("not shapingConn")
+		}
+		validateCountAndErr := func(count int, err error) {
+			if !errors.Is(err, expected) {
+				t.Fatal("unexpected err", err)
+			}
+			if count != 0 {
+				t.Fatal("expected zero")
+			}
+		}
+		validateCountAndErr(conn.Read(make([]byte, 16)))
+		validateCountAndErr(conn.Write(make([]byte, 16)))
+	})
+}