Remove unnecessary validation avoiding N+1 queries when building
integrations. This is a follow-up to fix
https://gitlab.com/gitlab-org/gitlab/-/issues/326209 where find or
initialize services causes N+1 queries.

Find or initialize the services has the following precedence:
- Find existing records.
- Build services from instance-level record or service template record.
  => This commit fixes the N+1 here.
- Build services from scratch. Fixed
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/58879.

In this case, when building one integration from an instance-level
integration or service template we check for service.invalid? which
triggers a query. service is an in-memory object but it checks the
uniqueness by type and project.  We can remove this because it's
redundant:
- All the integration records should be valid, we worked to verified
  that https://gitlab.com/groups/gitlab-org/-/epics/3366.
- build_from_integration copy the active value from the instance-level
  or service template. So if that integration is inactive,
  service = integration.dup will copy active attribute as false.