The following article explains how the theme folders are structured: http://docs.telerik.com/kendo-ui/styles-and-layout/appearance-styling.
You are, most likely, using at least one theme (e.g., the Default). Once you check how this is implemented in your app, you can remove the folders for the other themes.
The images and textures folder are used by mobile widgets and for fallback, so you may remove them, but some fallbacks may not occur gracefully. This decision will depend on your target audience browsers. Generally, I would say that you should remove only the themes you do not use, but keep the images and textures folders.
As for the scripts—this will, again, depend on what you use in your project. For example, if you reference kendo.all.min.js everywhere, you can remove just about all the scripts (you may want to leave cultures and messages or parts of them if you use the localization features). The following article lists the scripts and how they are used so you can see what you use and what you need: http://docs.telerik.com/kendo-ui/intro/installation/what-you-need.
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