Remove the `User#is_admin?` method

What does this MR do?

It removes the is_admin? method from the user.rb since there already is a boolean admin field in the users table.

What are the relevant issue numbers?

Closes #30584 (closed)

@rspeicher, should is_admin be changed in APIv3?

@blackst0ne No, API will need to stay the same.

added 1 commit

• 9c3f0edf - Remove the User#is_admin? method

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added 714 commits

• 9c3f0edf...7d3f37b0 - 713 commits from branch gitlab-org:master
• d401c485 - Remove the User#is_admin? method

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unmarked as a Work In Progress

1. I have not touched any API responses.
2. The failed spec seems to be not mine (I rebased on the master before pushing the code).
3. The code is ready for review.

assigned to @rspeicher

@blackst0ne Can you take a look at the spec failures? They don't look related but I'm not sure, and I've not seen them before.

assigned to @blackst0ne

added 4 commits

• d401c485...40407764 - 3 commits from branch gitlab-org:master
• a0d1253a - Remove the User#is_admin? method

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added 89 commits

• a0d1253a...3d1cade1 - 88 commits from branch gitlab-org:master
• 362f5e91 - Remove the User#is_admin? method

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added 1 commit

• 11aff97d - Remove the User#is_admin? method

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@rspeicher, I fixed that.

assigned to @rspeicher

added ~164274 label

changed milestone to %9.1

merged

mentioned in commit 5e1a802b

@blackst0ne Thanks! There were a few EE-only usages I cleaned up in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1615.

mentioned in issue #30682 (moved)

mentioned in issue gitlab#9189