The solution is simple to remove frequent folders from ms-explorer in quick access on Windows-10!
Please start the MS-Explorer for example via keyboard shortcut Windows-Logo + E and select the menu point View.
In explorer view settings open Folder Options  and the Tab General.
Uncheck the check-boxes:
[ ] Show frequently used folders in Quick access
[ ] Show recently used files in Quick access
(... see Image-1 Arrow 1 to 6)
While browsing folders in the Windows-10 Computer folder, you can apply the current view setting to all folders on your computer that are optimized for the same content as the folder you have open. For instance, the My Pictures folder is optimized for picture files. If you open this folder and change the view to Large Icons, you can apply the Large Icons view to every folder that's optimized for pictures in Windows-10.
To change the type of file that a folder is optimized for, right-click the folder, click Properties, click the Customize tab, click a file type in the Optimize this folder for list, and then click OK.
FAQ 34: Updated on: April 16th 2015 23:06