Stop creating GitlabIssueTrackerService records

What does this MR do?

I'm working towards removing the GitlabIssueTrackerService class. In order to do so, I want to delete all records of type GitlabIssueTrackerService in the services table. The migration to remove those will follow in a later iteration. This MR should make sure no new records will be created.

It should avoid a situation where all records get deleted on canary but another node running older code, creates new records.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team