chore: remove Repetier settings leftovers

[jacopotediosi]

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What does this PR do and why is it necessary?

1. Remove ignoreIdenticalResends and identicalResendsCountdown settings leftovers from config schema, Settings API, and UI. They were removed by 86b886e in 2018.
2. Remove swallowOkAfterResend setting leftover from Settings API. It was introduced in 2013 by d12da25, and later removed in 2015 by 116a540.

This was dead code since years, so of course it's bugfix release relevant.

How was it tested? How can it be tested by the reviewer?

No need to test, this was all dead code.
Edit: CI here failed because of a bug in unit tests (see #5332). Actually, pytest passes on my laptop.

Was any kind of genAI (ChatGPT, Copilot etc) involved in creating this PR? Which one and how?

No.

Any background context you want to provide?

What are the relevant tickets if any?

Screenshots (if appropriate)

Further notes