Remove submission from leaderboad

[ihsaan-ullah]

Todos:

• fix empty error when admin is removing someone else's submission

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I want to remove a submission for leaderboard. There are two problems:

1. Whan an admin wants to do that (for his own submission), it says this:

2. When an admin wants to do it for someone else's submission, this is shown

[Didayolo]

I think it is not a big problem if admins can't remove a submission from the leaderboard if it is not allowed by the setting of the competition. Of course the blank error message is problematic.