Update interfaces/speech-api.idl (#18289)

Source: https://github.com/tidoust/reffy-reports/blob/acde19a/whatwg/idl/speech-api.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/568218224

Author: autofoolip

interfaces/speech-api.idl

@@ -90,7 +90,7 @@ dictionary SpeechRecognitionEventInit : EventInit {
 };
 
 // The object representing a speech grammar
-[Exposed=Window, Constructor]
+[Exposed=Window]
 interface SpeechGrammar {
     attribute DOMString src;
     attribute float weight;