Address vue/no-unused-properties violations

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What does this MR do and why?

Adresses vue/no-unused-properties violation in:

• app/assets/javascripts/projects/settings/branch_rules/components/edit/protections/merge_protections.vue
• app/assets/javascripts/projects/settings/branch_rules/components/edit/protections/push_protections.vue
• app/assets/javascripts/projects/settings/components/branch_rule_modal.vue
• app/assets/javascripts/projects/settings/repository/branch_rules/app.vue
• app/assets/javascripts/projects/settings_service_desk/components/custom_email_form.vue
• app/assets/javascripts/projects/settings_service_desk/components/service_desk_setting.vue

References

Fixes #525756 (closed)