Variables starting with `u' in src/od-amiga

• use_approx_color src/od-amiga/ami-win.c:201
• usecyb src/od-amiga/ami-win.c:245
• use_delta_buffer src/od-amiga/ami-win.c:198
• use_graffiti src/od-amiga/ami-win.c:200
• usepub src/od-amiga/ami-win.c:244