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/engine/netx/dialer/shaping_enabled.go

@@ -1,43 +0,0 @@
-//go:build shaping
-// +build shaping
-
-package dialer
-
-import (
-	"context"
-	"net"
-	"time"
-
-	"github.com/ooni/probe-cli/v3/internal/model"
-)
-
-// shapingDialer ensures we don't use too much bandwidth
-// when using integration tests at GitHub. To select
-// the implementation with shaping use `-tags shaping`.
-type shapingDialer struct {
-	model.Dialer
-}
-
-// DialContext implements Dialer.DialContext
-func (d *shapingDialer) DialContext(
-	ctx context.Context, network, address string) (net.Conn, error) {
-	conn, err := d.Dialer.DialContext(ctx, network, address)
-	if err != nil {
-		return nil, err
-	}
-	return &shapingConn{Conn: conn}, nil
-}
-
-type shapingConn struct {
-	net.Conn
-}
-
-func (c *shapingConn) Read(p []byte) (int, error) {
-	time.Sleep(100 * time.Millisecond)
-	return c.Conn.Read(p)
-}
-
-func (c *shapingConn) Write(p []byte) (int, error) {
-	time.Sleep(100 * time.Millisecond)
-	return c.Conn.Write(p)
-}