gui: Remove tooltip shown over whole modal

Changed the attribute 'title' (reserved) to 'heading' for the modal
template

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3281

gui/default/syncthing/core/upgradingDialogView.html

@@ -1,3 +1,3 @@
-<modal id="upgrading" status="info" icon="arrow-circle-up" title="{{'Upgrading' | translate}}">
+<modal id="upgrading" status="info" icon="arrow-circle-up" heading="{{'Upgrading' | translate}}">
 	<p><span translate>Syncthing is upgrading.</span> <span translate>Please wait</span>...</p>
 </modal>