packages/DOS/common.dj: remove COFF debug info generation

gcc on DOS hasn't really supported COFF-debug (-gcoff) on djgpp for a
long time.

"Sounds like the COFF debug info generation has bit-rotted in GCC.
 Nothing new here, no other platform uses COFF AFAIK."

So lets drop it too.

URL: http://curl.haxx.se/mail/lib-2013-01/0130.html

packages/DOS/common.dj

@@ -92,7 +92,7 @@ ARES_ROOT    = $(TOPDIR)/ares
 CC   = gcc
 YACC = bison -y
 
-CFLAGS = -g -gcoff -O2 -I. -I$(TOPDIR)/include -I$(TOPDIR)/lib \
+CFLAGS = -g -O2 -I. -I$(TOPDIR)/include -I$(TOPDIR)/lib \
          -I$(WATT32_ROOT)/inc -Wall -DHAVE_CONFIG_H
 
 ifeq ($(USE_SSL),1)