Bug 11513: (follow-up) format enrollment end date consistently

Bug 11513: (follow-up) format enrollment end date consistently

The previous patch added use of the KohaDates TT plugin, so this
patch makes sure that it gets used to format the display of all
occurrences of the enrollment end date.

To test:

[1] Create a patron category with a fixed end date.
[2] Bring up the list of all categories and verify that the date
    is displayed based on the dateformat value.
[3] Delete the category, and verify that the confirmation dialog
    formats the date correctly.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>