ext.uls.eventlogger: Remove unused code

Follows-up e58be7c411, 1ad0c9c819.

* The mw.uls.eventlogger property does not appear to be
  used anywhere indexed by Codesearch. It was also undocumented.
  Removed without deprecation. Kept exposed for debugging purpopses
  via module.exports, which could be retreived in tests via require(),
  or via mw.loader.require() from the browser console.

* Remove redundant $.Deferred wrapper.

Change-Id: Id081038e5d4902c7e38967353c6f551c12517311

.eslintrc.json

@@ -4,6 +4,9 @@
 		"wikimedia/client",
 		"wikimedia/jquery"
 	],
+	"env": {
+		"commonjs": true
+	},
 	"globals": {
 		"mw": false,
 		"OO": false