fix module unlock date with i18n

test plan:
* enable localization and choose a language for the course
 with a different date format (e.g. Japanese)
* create a module and set an unlock date
* reload the page
* try to edit the module
* confirm that it did not localize the date inside the input box,
 thus breaking the form

closes #CNVS-14984

Change-Id: Ice4b4d83c9bffa06d3292b123c2e10c632801718
Reviewed-on: https://gerrit.instructure.com/42177
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>