Revert "[r21246]Allow hard-coded paths to be overridden with $XDG_DATA_DIRS"

This reverts r21247

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps40@21256 4ae1f11a-8b86-4847-b8af-ab372f36d1fd