Drop 'default' column from services table

Description

default column from services table is only set to true for GitLabIssueTrackerService.

We can drop the column after removing GitLabIssueTrackerService and some of the scopes used by it !28219 (comment 340743964).

This issue is blocked by !28219 (closed), !34852 (merged), !36063 (merged).

Releases

https://docs.gitlab.com/ee/development/what_requires_downtime.html#dropping-columns

Removing columns is tricky because running GitLab processes may still be using the columns. To work around this safely, you will need three steps in three releases:

• Ignoring the column %13.3 !38203 (merged)
• Dropping the column %13.4 !39817 (merged)
• Removing the ignore rule %13.5 !42688 (merged)