[CI] Remove needless ci/docker/ubuntu-22.04-csharp.dockerfile

[kou]

Describe the enhancement requested

https://github.com/apache/arrow/blob/main/ci/docker/ubuntu-22.04-csharp.dockerfile

I should have removed it in #47547 ...

Component(s)

Continuous Integration

[kou]

Issue resolved by pull request 48298
#48298