[FIX] l10n_de: translation issues

There was inconsistency in the translation for the words "price unit", with this
 commit all the "price unit" are translated the same.

closes odoo/odoo#134107

Task-id: 3262408
Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>
Signed-off-by: Maximilien La Barre (malb) <malb@odoo.com>