[Coco] continuing to eliminate errors in the nitros9 build

[Bob Devries]

Removing some warnings:

in file /nitros9/level2/coco3/makefile

at label:

DSKS:

    $(DSKDW) is duplicated

LDSKS:

    $(LDSKDW) is duplicated

Regards, Bob Devries
Dalby, QLD, Australia