dist/tools/kconfiglib: Add remove command to delete files
dist/tools/kconfiglib: Add remove command to delete files

The 'remove' target removes the downloaded files from the tool.

RIOT-OS/RIOT,authmillenon/RIOT,kYc0o/RIOT,ant9000/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,basilfx/RIOT,ant9000/RIOT,kYc0o/RIOT,miri64/RIOT,miri64/RIOT,kYc0o/RIOT,basilfx/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,ant9000/RIOT,kYc0o/RIOT,OTAkeys/RIOT,jasonatran/RIOT,kaspar030/RIOT,kYc0o/RIOT,basilfx/RIOT,miri64/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,jasonatran/RIOT,miri64/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,miri64/RIOT,jasonatran/RIOT,authmillenon/RIOT,authmillenon/RIOT,ant9000/RIOT,basilfx/RIOT,jasonatran/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kaspar030/RIOT,authmillenon/RIOT,ant9000/RIOT,kaspar030/RIOT,basilfx/RIOT