uniflash.inc.mk: remove `export` from `UNIFLASH_PATH`
uniflash.inc.mk: remove `export` from `UNIFLASH_PATH`

Signed-off-by: Jean Pierre Dudey <341388fa1817ca285e65547384a9727ce7f6d39a@hotmail.com>

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