Remove javascripts/pages/admin/services directory

What does this MR do and why?

Removes the javascripts/pages/admin/services directory.

Service templates were deprecated in GitLab 14.0. This directory is a left-over artifact of this deprecation. It is not used.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

To triple check, you can try setting up an admin-level integration to make sure it still works.

https://docs.gitlab.com/ee/user/admin_area/settings/project_integration_management.html

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #346327 (closed)