Revert "Throw an error and hint if SYMLINK is defined on the command-line"

This reverts commit cfcff881

src/sbbs3/GNUmakefile

@@ -11,10 +11,6 @@
 # Optional build targets: dlls, utils, mono, all (default)				#
 #########################################################################
 
-ifdef SYMLINK
-$(error SYMLINK was defined and unexpected. You might mean the 'symlinks' target instead)
-endif
-
 PWD	:=	$(shell /bin/pwd)
 SRC_ROOT	?=	${PWD}/..
 include $(SRC_ROOT)/build/Common.gmake