Removed empty unit date element

Markup on <unitdate era="ce" calendar="gregorian"/> this is on line 85
in the file.

git-svn-id: https://subversion.lib.virginia.edu/repos/ead/branches/pub-schema/uva-sc@10807 6d43c525-cd11-0410-ac62-a67304e79d8a
Merge branch 'pub-schema' of https://github.com/uvalib-dcs/VH_uva-sc into pub-schema
(merge lorrie's changes)

git-svn-id: https://subversion.lib.virginia.edu/repos/ead/branches/pub-schema/uva-sc@10831 6d43c525-cd11-0410-ac62-a67304e79d8a