Redmine

When removing user(s) from a group via Administration > Groups > (group) > Users tab,
clicking the "Remove" link now shows a confirmation page (introduced in #43640) that
displays "Translation missing: en.text_users_remove_from_group_confirmation" instead of
a proper confirmation message.

Steps to reproduce:
1. Go to Administration > Groups
2. Open a group that has one or more users
3. On the Users tab, click the remove (unlink) icon next to a user
4. On the confirmation page (/groups/:id/users?user_id=X), the warning text shows
"Translation missing: en.text_users_remove_from_group_confirmation"

Root cause:
The confirmation page was added in #43640 (app/views/groups/remove_users.erb),
which references the locale key `text_users_remove_from_group_confirmation`.
However, this key was never added to config/locales/en.yml (or any other locale
file), so it falls back to the "translation missing" placeholder for every
language, including English itself.

This is confirmed still present on current trunk/master.

Related to #43640.

Patch attached (adds the missing key to en.yml and ja.yml).