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/usagereport/usageReportPreviewModalView.html

@@ -1,4 +1,4 @@
-<modal id="urPreview" status="success" icon="bar-chart" title="{{'Anonymous Usage Reporting' | translate}}" large="yes" close="yes" tabindex="-1">
+<modal id="urPreview" status="success" icon="bar-chart" heading="{{'Anonymous Usage Reporting' | translate}}" large="yes" close="yes" tabindex="-1">
   <p translate>The encrypted usage report is sent daily. It is used to track common platforms, folder sizes and app versions. If the reported data set is changed you will be prompted with this dialog again.</p>
   <p translate translate-value-url="<a href=&quot;https://data.syncthing.net&quot; target=&quot;_blank&quot;>https://data.syncthing.net</a>">The aggregated statistics are publicly available at {%url%}.</p>
   <form>