Updated German translation.

For plural forms, the singular does not need to specify the %d conversion specifier.
See e.g. this thread http://article.gmane.org/gmane.comp.version-control.git/221583

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/branches/2.4@22913 57a11ea4-9604-0410-9ed3-97b8803252fd