Remove broken link in grade school. fixes #2040

[ceddlyburge]

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[ceddlyburge]

Hi @SaschaMann @ErikSchierboom this change fails the configlet CI check when I sync it in to the Elm repository.
https://github.com/exercism/elm/runs/6536869034?check_suite_focus=true

Can we fix this by just removing source, or will we need to update configlet?

Thanks, Cedd

[ee7]

@ceddlyburge Ah. It turns out that configlet sync doesn't properly handle a key/value pair that was removed.

I'll fix configlet so that configlet sync -u removes a source or source_url property (rather than setting the value to the empty string) from an exercise's .meta/config.json if the corresponding key was removed in problem-specifications.

For now, please remove source_url manually.

---

I've checked that this PR was the first time we've removed a source or source_url key since Exercism v3. That's why we didn't hit this edge case for configlet sync before.

cd /tmp
git clone https://github.com/exercism/problem-specifications
cd problem-specifications
git checkout 05999f3
git log --oneline -- 'exercises/*/metadata.toml'

• 05999f3 Remove broken link in grade school. fixes #2040
• 7cd0ab1 Add exercise: killer-sudoku-helper
• 3e1cfcb Add exercise: state-of-tic-tac-toe
• 2b039c3 Fix bowling game copy
• d2a4b3e Two-fer: add title to metadata
• df6420b Convert exercise metadata from yaml to toml