Update revoke invite modal title and remove unneeded checkbox

📖 What does this MR do?

Related to #259794 (closed)

Updates the title of the revoke user invite modal. Also removes the Also unassign this user from related issues and merge requests checkbox since this checkbox doesn't make sense in this context. Invited users don't have a GitLab account yet so there is no way for them to own any issues or merge requests.

💻 Local testing

1. Create a group or project
2. Navigate to that newly created group or project
3. In the Search for members to update or invite field enter an email of a user that does not yet exist. Click Invite.
4. In the Invited tab click the Revoke invite button

📷 Screenshots

Before	After

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