Since the HTML5 Report Viewer uses Kendo UI for its default template it is possible to use it even with a custom build instead of using the shipped Kendo bundle. There are two ways to create a custom build - with Kendo UI Custom Download Builder and using gulp build tool
Below you can find the list of widgets that the HTML5 Report Viewer requires in order to work properly. In case you edit the template and remove a widget you can subtract it from this list as well. Note that the widgets have other dependencies. The Touch widget is required only for the gestures. All widgets except the TreeView can be found in Kendo UI Core. The TreeView is in Kendo UI Professional.
Kendo TreeView (pro)
Kendo UI Professional license is not required if you are only going to use the demanded pro widgets for the needs of HTML5 Report Viewer. Telerik Reporting provides a JS file containing a subset of the used by default Kendo UI widgets - telerikReportViewer.kendo-22.214.171.1245.min.js. The subset is build with Telerik Kendo UI R2 2018 SP1 (2019.1.115) that requires jQuery 1.12.4 and is also compatible with 1.10.x, 2.2.x and 3.3.1. For more information refer to Telerik Reporting License Agreement (point 4.2).