gadget.txt: remove requiresES6

Removed in MediaWiki 1.42. This option doesn't seem to do anything anymore.

https://phabricator.wikimedia.org/T75714#9443736

gadget.txt

@@ -1,4 +1,4 @@
-* Twinkle [ResourceLoader |dependencies=ext.gadget.morebits, ext.gadget.select2, mediawiki.api, mediawiki.language |rights=autoconfirmed |type=general |peers=Twinkle-pagestyles |requiresES6] |Twinkle.js |Twinkle.css |twinklearv.js |twinklewarn.js |twinkleblock.js |twinklewelcome.js |twinkleshared.js |twinkletalkback.js |twinklespeedy.js |twinkleprod.js |twinklexfd.js |twinkleimage.js |twinkleprotect.js |twinkletag.js |twinklediff.js |twinkleunlink.js |twinklerollback.js |twinkledeprod.js |twinklebatchdelete.js |twinklebatchprotect.js |twinklebatchundelete.js |twinkleconfig.js
-* morebits [ResourceLoader |dependencies=mediawiki.user, mediawiki.util, mediawiki.Title, jquery.ui |hidden |requiresES6] |morebits.js |morebits.css
+* Twinkle [ResourceLoader |dependencies=ext.gadget.morebits, ext.gadget.select2, mediawiki.api, mediawiki.language |rights=autoconfirmed |type=general |peers=Twinkle-pagestyles] |Twinkle.js |Twinkle.css |twinklearv.js |twinklewarn.js |twinkleblock.js |twinklewelcome.js |twinkleshared.js |twinkletalkback.js |twinklespeedy.js |twinkleprod.js |twinklexfd.js |twinkleimage.js |twinkleprotect.js |twinkletag.js |twinklediff.js |twinkleunlink.js |twinklerollback.js |twinkledeprod.js |twinklebatchdelete.js |twinklebatchprotect.js |twinklebatchundelete.js |twinkleconfig.js
+* morebits [ResourceLoader |dependencies=mediawiki.user, mediawiki.util, mediawiki.Title, jquery.ui |hidden] |morebits.js |morebits.css
 * Twinkle-pagestyles [hidden |skins=vector, vector-2022] |Twinkle-pagestyles.css
 * select2 [ResourceLoader |hidden] |select2.min.js |select2.min.css