Remove unused ktau from biogeochem

[Whyborn]

CABLE

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Description

Removes ktau from all calls to biogeochem at the call site and routine definition, as it was unused. Has no effect on the results, see benchcab run at /scratch/rp23/lw5085/bench_example.

2026-01-08 16:05:28,009 - INFO - benchcab.benchcab.py:391 - 0 failed, 168 passed

Fixes #(668)

Type of change

• Code clean up

Checklist

• The new content is accessible and located in the appropriate section
• I have checked that links are valid and point to the intended content
• I have checked my code/text and corrected any misspellings

Testing

• Are the changes bitwise-compatible with the main branch? If working on an optional feature, are the results bitwise-compatible when this feature is off? If yes, copy benchcab output showing successful completion of the bitwise compatibility tests or equivalent results below this line.

Please add a reviewer when ready for review.

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📚 Documentation preview 📚: https://cable--669.org.readthedocs.build/en/669/