fix(german_250k.json): remove non-german accents (@8e3) (monkeytypegame#6756)

Removed non-German accents / untypable loanwords

### Description

Since the German qwertz layout doesn't support certain accents, used in
some loanwords in this list, typing them is impossible, without changing
your keyboard layout mid-session. Using an automated script, I decided
to remove them, enhancing playability.

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Co-authored-by: fehmer <[email protected]>

Author: 8e3