examples/filesystem: blacklist feature instead of boards
examples/filesystem: blacklist feature instead of boards

Remove BOARD_BLACKLIST and use FEATURES_BLACKLIST instead.

kaspar030/RIOT,OlegHahm/RIOT,yogo1212/RIOT,smlng/RIOT,basilfx/RIOT,mtausig/RIOT,basilfx/RIOT,authmillenon/RIOT,x3ro/RIOT,josephnoir/RIOT,x3ro/RIOT,jasonatran/RIOT,toonst/RIOT,jasonatran/RIOT,aeneby/RIOT,mtausig/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,x3ro/RIOT,OTAkeys/RIOT,basilfx/RIOT,kYc0o/RIOT,miri64/RIOT,yogo1212/RIOT,mtausig/RIOT,OTAkeys/RIOT,josephnoir/RIOT,aeneby/RIOT,RIOT-OS/RIOT,miri64/RIOT,ant9000/RIOT,jasonatran/RIOT,smlng/RIOT,authmillenon/RIOT,authmillenon/RIOT,mtausig/RIOT,yogo1212/RIOT,kaspar030/RIOT,kYc0o/RIOT,toonst/RIOT,aeneby/RIOT,OlegHahm/RIOT,authmillenon/RIOT,authmillenon/RIOT,smlng/RIOT,smlng/RIOT,jasonatran/RIOT,ant9000/RIOT,smlng/RIOT,aeneby/RIOT,toonst/RIOT,mtausig/RIOT,x3ro/RIOT,miri64/RIOT,yogo1212/RIOT,OTAkeys/RIOT,toonst/RIOT,kYc0o/RIOT,aeneby/RIOT,kYc0o/RIOT,x3ro/RIOT,kaspar030/RIOT,yogo1212/RIOT,OTAkeys/RIOT,ant9000/RIOT,OlegHahm/RIOT,yogo1212/RIOT,josephnoir/RIOT,ant9000/RIOT,miri64/RIOT,kYc0o/RIOT,OTAkeys/RIOT,josephnoir/RIOT,basilfx/RIOT,basilfx/RIOT,authmillenon/RIOT,toonst/RIOT,jasonatran/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT