remove all externalContentReady on close

fixes PLAT-1428, PLAT-1805

test plan:
create an assignment
select a cotent-item tool from the RCE
cancel the selection by closing the modal
select the external tool for submission type
there shouldn't be any items in the RCE

Change-Id: I19c3bac821f470b8754ace9879f8a8a43fb6a19f
Reviewed-on: https://gerrit.instructure.com/90326
Tested-by: Jenkins
Reviewed-by: Weston Dransfield <wdransfield@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Nathan Mills <nathanm@instructure.com>

public/javascripts/tinymce_plugins/instructure_external_tools/initializeExternalTools.js

@@ -140,6 +140,7 @@ define([
         close: function(){
           $dialog.find("iframe").attr('src', '/images/ajax-loader-medium-444.gif');
           $(window).off('beforeunload', ExternalToolsPlugin.beforeUnloadHandler);
+          $(window).unbind("externalContentReady");
         }
       });
       $(window).on('beforeunload', ExternalToolsPlugin.beforeUnloadHandler);

spec/coffeescripts/tinymce_plugins/instructure_external_tools/initializeExternalToolsSpec.coffee

@@ -71,3 +71,18 @@ define [
       }
     }] } )
     ok ExternalToolsPlugin.dialogCancelHandler.notCalled
+
+  test "it removes the externalContentReady handler on close", ()->
+    externalContentReadySpy = sinon.spy()
+    ExternalToolsPlugin.dialogCancelHandler = ()->
+    $dialog = ExternalToolsPlugin.buttonSelected(@buttonSpy, @fakeEditor)
+    $(window).bind("externalContentReady", externalContentReadySpy)
+    $dialog.dialog('close')
+    $(window).trigger("externalContentReady", { contentItems: [{
+      "@type": 'LtiLinkItem',
+      url: 'http://canvas.instructure.com/test',
+      placementAdvice: {
+        presentationDocumentTarget: ""
+      }
+    }] } )
+    ok externalContentReadySpy.notCalled