(core) Some cleanup: remove old unused modules.

Summary:
- Remove modules related to old login / profile that we don't plan to bring back.
- Remove old unused DocListModel.
- Remove ext* tests that have been skipped and don't work.
- Remove old ModalDialog, and switch its one remaining usage to the newer way.

Test Plan: All tests should pass, and as many as before.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2668

app/client/exposeModulesForTests.js

@@ -7,7 +7,6 @@ Object.assign(window.exposedModules, {
   ko: require('knockout'),
   moment: require('moment-timezone'),
   Comm: require('./components/Comm'),
-  ProfileForm: require('./components/ProfileForm'),
   _loadScript: require('./lib/loadScript'),
   ConnectState: require('./models/ConnectState'),
 });