Don't warn on unload in iframe

CHANGELOG.md

@@ -1,5 +1,8 @@
 # (Unreleased; add upcoming change notes here)
 
+- Fix one last case where the user might be warned unnecessarily when navigating
+  away from iodide (#2884)
+
 # 0.20 (2020-05-23)
 
 - Allow creating iodide notebook with attached files via a POST request, using

src/eval-frame/index.jsx

@@ -20,7 +20,6 @@ import messagePasserEval from "../shared/utils/redux-to-port-message-passer";
 import { iodide } from "./iodide-api/api";
 
 import "./port-to-editor";
-import { handleInterceptBackspace } from "../shared/intercept-keybindings";
 
 messagePasserEval.connectDispatch(store.dispatch);
 window.iodide = iodide;
@@ -43,6 +42,5 @@ render(
   document.getElementById("view-mode-styles")
 );
 
-handleInterceptBackspace();
 // initializeUserVariables() **MUST** be the last line of this file!
 initializeUserVariables();