Bug 1520663 - enable blocking autoplay with user-gesture-activation model on Fennec. r=cpearce

Differential Revision: https://phabricator.services.mozilla.com/D16773

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

mobile/android/app/mobile.js

@@ -581,15 +581,10 @@ pref("media.mediasource.enabled", true);
 
 pref("media.mediadrm-widevinecdm.visible", true);
 
-#ifdef NIGHTLY_BUILD
 // Switch block autoplay logic to v2.
 pref("media.autoplay.enabled.user-gestures-needed", true);
 // Set Fennec to block autoplay by default.
 pref("media.autoplay.default", 1); // 0=Allowed, 1=Blocked
-#else
-pref("media.autoplay.default", 0); // 0=Allowed, 1=Blocked
-pref("media.autoplay.enabled.user-gestures-needed", false);
-#endif
 
 // Enable WebSpeech speech synthesis
 pref("media.webspeech.synth.enabled", true);