Remove JetBrains Space from Dart package repositories as a service section in custom-package-repositories

[ali-alizadeh]

Given JetBrains Space's pivot to SpaceCode, which will not include package management functionality as confirmed in the official migration documentation, I think SpaceCode should no longer be recommended for teams or projects that require integrated package management solutions.

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[parlough]

Thanks for updating this!

A little sad 😢

[parlough]

/gcbrun

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