makefiles/tools/uniflash.inc.mk: remove empty RESET_FLAGS
makefiles/tools/uniflash.inc.mk: remove empty RESET_FLAGS

Remove the line with only 'RESET_FLAGS'. This was a migration mistake
when removing 'export'.

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