doc: Remove autodoc-process-signature hook

[dweindl]

By now, this is redundant with the ast-postprocessing of the swig-wrapper.

Related to #2399.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.40%. Comparing base (2732898) to head (ebbc2ec).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3029      +/-   ##
==========================================
- Coverage   78.03%   77.40%   -0.64%     
==========================================
  Files         311      311              
  Lines       20587    20587              
  Branches     1499     1499              
==========================================
- Hits        16066    15935     -131     
- Misses       4511     4642     +131     
  Partials       10       10              

Flag	Coverage Δ
cpp	70.33% <ø> (ø)
cpp_python	36.75% <ø> (ø)
petab	45.72% <ø> (ø)
petab_sciml	13.66% <ø> (ø)
python	69.33% <ø> (ø)
sbmlsuite-jax	?

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see 6 files with indirect coverage changes

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