Members view - update revoke invite modal header and button

Follow-up to !43919 (merged)

Currently the header and button in the "Revoke invite" modal don't really make sense.

The header and button should be changed to Revoke invite. Also I don't think we need the "Also unassign this user from related issues and merge requests" checkbox as this user isn't a member yet. Need to double check on that though.

Current

Proposed

Implementation plan

1. Add isInvite prop to app/assets/javascripts/members/components/action_buttons/remove_member_button.vue#L33
2. Add data-is-invite attribute to app/assets/javascripts/members/components/action_buttons/remove_member_button.vue#L53
3. Add isInvite computed property to app/assets/javascripts/vue_shared/components/remove_member_modal.vue#L24
4. Update app/assets/javascripts/vue_shared/components/remove_member_modal.vue#L26 to account for isInvite computed property.
5. Hide app/assets/javascripts/vue_shared/components/remove_member_modal.vue#L73 if isInvite is true