Remove gitlab-pages daemon

What does this MR do?

Deprecate daemon-uid and daemon-gid and disable support for "daemon mode"

Closes #133 (closed)
Closes #114 (closed)

Blocked by !536 (merged)
Blocked by !541 (merged)
Blocked by omnibus-gitlab!5639 (merged)

This MR should not be merged until omnibus-gitlab#6381 (closed) is completed.

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines