switch to Promise.all

MediaBrowser.WebDashboard/MediaBrowser.WebDashboard.csproj

@@ -659,9 +659,6 @@
     <Content Include="dashboard-ui\syncsettings.html">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
-    <Content Include="dashboard-ui\apiclient\ajax.js">
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </Content>
     <Content Include="dashboard-ui\apiclient\alt\bean.js">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>