Manager: make artificial API delay actually optional

For development of the web interface, to get a less predictable order of
asynchronous requests, the API responses were artificially delayed. This
was supposed to be optional, to be enabled via the `-delay` CLI argument,
but somehow the optionalness either never made it in or was mysteriously
removed.

cmd/flamenco-manager/main.go

@@ -292,7 +292,9 @@ func buildWebService(
 	e.Use(middleware.Recover())
 
 	// For development of the web interface, to get a less predictable order of asynchronous requests.
+	if cliArgs.delayResponses {
 		e.Use(randomDelayMiddleware)
+	}
 
 	// Disabled, as it causes issues with "204 No Content" responses.
 	// TODO: investigate & file a bug report. Adding the check on an empty slice