DEV: Don't allow Promise unless imported from "rsvp"

We want to make sure we are using the correct promise implementation so
let's lint out the browser version.

app/assets/javascripts/discourse/lib/eyeline.js.es6

@@ -1,4 +1,5 @@
 import ENV from "discourse-common/config/environment";
+import { EventTarget } from "rsvp";
 
 //  Track visible elemnts on the screen.
 const Eyeline = function Eyeline(selector) {
@@ -70,6 +71,6 @@ Eyeline.prototype.flushRest = function() {
   $(this.selector).each((i, elem) => this.trigger("saw", { detail: $(elem) }));
 };
 
-RSVP.EventTarget.mixin(Eyeline.prototype);
+EventTarget.mixin(Eyeline.prototype);
 
 export default Eyeline;

app/assets/javascripts/discourse/routes/application.js.es6

@@ -12,6 +12,7 @@ import { findAll } from "discourse/models/login-method";
 import { getOwner } from "discourse-common/lib/get-owner";
 import { userPath } from "discourse/lib/url";
 import Composer from "discourse/models/composer";
+import { EventTarget } from "rsvp";
 
 function unlessReadOnly(method, message) {
   return function() {
@@ -288,5 +289,5 @@ const ApplicationRoute = DiscourseRoute.extend(OpenComposer, {
   }
 });
 
-RSVP.EventTarget.mixin(ApplicationRoute);
+EventTarget.mixin(ApplicationRoute);
 export default ApplicationRoute;

app/assets/javascripts/discourse/routes/topic.js.es6

@@ -6,6 +6,7 @@ import { later } from "@ember/runloop";
 import DiscourseRoute from "discourse/routes/discourse";
 import DiscourseURL from "discourse/lib/url";
 import { ID_CONSTRAINT } from "discourse/models/topic";
+import { EventTarget } from "rsvp";
 
 let isTransitioning = false,
   scheduledReplace = null,
@@ -313,5 +314,5 @@ const TopicRoute = DiscourseRoute.extend({
   }
 });
 
-RSVP.EventTarget.mixin(TopicRoute);
+EventTarget.mixin(TopicRoute);
 export default TopicRoute;