[cleanup] Fix some warnings

Fix compiler warnings ocurring in DuMuX' test with ALUGrid when using Clang master (will be 15)

enabled an automatic merge when the pipeline for 129fb0d7 succeeds

canceled the automatic merge

added 2 commits

• 67a9df54 - [cleanup] Remove unused variables
• 22dc5932 - [cleanup] Remove German umlaut from comment

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added 1 commit

• 7aed4e08 - [cleanup] Remove German umlaut from comment

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I added two more commits for warnings emitted by more recent Clang 15 (not yet released).

mentioned in merge request !144 (merged)

Thanks @gruenich for cleaning up this! And sorry for not responding so long, was away for most of August.

I pushed to a branch in extensions/dune-alugrid in order to see the pipeline running, and will merge when pipeline succeeds.

!144 (merged)

closed

@samuel.burbulla Thank you for taking care! Much appreciated.

@gruenich, @samuel.burbulla: Actually, this kind of white spaces changes are currently not welcome, because it makes the upcoming merge of the twist free grid more difficult. Especially since this concerns warnings of an compliler yet to be relased. I will potentially revert the merge of !144 (merged) if the conflict resolving takes to much time.

resolved all threads