Revert "Mac OS X option"

This reverts commit 69af8d5.

Author: takano32

mk.bash

@@ -6,9 +6,6 @@ OS=$(uname -s)
 if [[ $OS = "OpenBSD" ]];then
 	echo "using OpenBSD Makefile."
 	make -f makefile.openbsd
-elif [[ $OS = "Darwin" ]];then
-        echo "using Mac OS X Makefile."
-        make -f makefile.macosx
 else
 	echo "using Linux Makefile."
 	make -f makefile