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/dialer.go

@@ -67,6 +67,5 @@ func New(config *Config, resolver model.Resolver) model.Dialer {
 	if config.ContextByteCounting {
 		d = &byteCounterDialer{Dialer: d}
 	}
-	d = &shapingDialer{Dialer: d}
 	return d
 }