Pages: Settings page delete button label should be 'Delete Pages'

Summary

The delete button on the Pages settings page uses incorrect wording. It should read "Delete pages" to be consistent with GitLab's UI conventions and to clearly communicate the action to users.

Steps to reproduce

1. Navigate to a project's Pages settings page
2. Observe the label on the delete button

Expected behavior

The button label should be "Delete Pages".

Actual behavior

The button label uses different wording (not "Delete pages").

Additional context

Identified during Vue 3 migration (vue3_migrate_pages feature flag) review. The issue is unrelated to the Vue 3 migration itself.