If you are truly not using any ajax control or Telerik RadControl you can turn off the inclusion of the RadScriptManager by going to the page advanced options (see the attached image).
Have in mind that even if you have unselected this checkbox but you still have control(s) that requires a script manager (a script control) the RadScriptManager will be included in the page and the Telerik.Web.UI script will be loaded. An example of the case is the scenario in which while browsing the page you are logged as a backed user with sufficient rights to edit a page. This means that you have browse and edit enabled on the page you are viewing. The interface for the browse and edit includes RadControls and therefore you will see this script being loaded no matter what you have on the page or whether you have enabled the RadScriptManager or not.
All the best,
the Telerik team
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