Bug 1598738 - Remove using namespace std from OnlineSpeechRecognitionService. r=andrenatal

Differential Revision: https://phabricator.services.mozilla.com/D54349

--HG--
extra : moz-landing-system : lando

dom/media/webspeech/recognition/OnlineSpeechRecognitionService.cpp

@@ -39,7 +39,6 @@
 namespace mozilla {
 
 using namespace dom;
-using namespace std;
 
 #define PREFERENCE_DEFAULT_RECOGNITION_ENDPOINT \
   "media.webspeech.service.endpoint"