Revert "mk/default.mk: Restore datadir."

This reverts commit ded873cb8fbf91c98eeab5d187eda57a1e773005.

mk/default.mk

@@ -13,9 +13,6 @@ prefix	= /usr/share
 # Where local lisp files go.
 lispdir= $(prefix)/emacs/site-lisp/org
 
-# Where local data files go.
-datadir = $(prefix)/emacs/etc/org
-
 # Where info files go.
 infodir = $(prefix)/info