gitk: spanish translation of gitk introduced extra directory

It seems as if commit cc398a286b4cb5cb76c515588668bab4858a01cf
(gitk: Spanish translation of gitk) introduced an extra directory.

Instead of creating gitk-git/po/es.po that commit created
gitk-git/gitk-git/po/es.po.  In other words, we need the following:

    git mv gitk-git/gitk-git/po/es.po gitk-git/po

Additionally, given that this will leave an empty directory
(gitk-git/gitk-git/po) that even "git clean -f" won't remove,
is it worth updating "git mv" so that it removes directories
if/when it removes all content from that directory?

- Eric