The cause for this in many cases is the inclusion of the built-in Search Box widget (web forms).
The first thing anyone would try is to disable the search suggestions by editing the SearchBox widget and going to its Advanced settings and setting DisableSuggestions
to True as below:
Unfortunately this does not prevent the kendo.all.min.js from loading.
The next thing to do is to actually check the html code of the default SearchBox widget.
If you scroll down a bit on the above screen you will see the LayoutTemplatePath property which points to:
This means we need to open the Telerik.Sitefinity.Resources.dll with JustDecompile and find the above embedded resource.
The code is pretty simple, yet powerful (loads a lot of stuff ;))
As you can see there is a reference to jQuery and to KendoAll libraries.
To get rid of the the KendoAll library the process is pretty simple - copy the code from above, remove the reference to KendoAll library and save it as a user control (.ascx) somewhere in your project, e.g. WidgetTemplates/SearchBox/SearchBox.ascx
Finally, edit the SearchBox widget, go to its Advanced settings and put the full path to your custom template in the LayoutTemplatePath property, e.g.
Of course if you want to use the search suggestions feature you would have to leave the above as it is.