Remove "experimental" warning for struct columns in ORC reader and writer

[vuule]

Description

Closes #11484

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov]

Codecov Report

Base: 87.40% // Head: 87.48% // Increases project coverage by +0.07% 🎉

Coverage data is based on head (87fcb47) compared to base (f72c4ce).
Patch coverage: 84.48% of modified lines in pull request are covered.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #11880      +/-   ##
================================================
+ Coverage         87.40%   87.48%   +0.07%     
================================================
  Files               133      133              
  Lines             21833    21864      +31     
================================================
+ Hits              19084    19128      +44     
+ Misses             2749     2736      -13     

Impacted Files	Coverage Δ
python/cudf/cudf/core/udf/__init__.py	50.00% <ø> (ø)
python/cudf/cudf/io/orc.py	92.94% <ø> (-0.09%)	⬇️
python/cudf/cudf/utils/ioutils.py	79.47% <ø> (ø)
...thon/dask_cudf/dask_cudf/tests/test_distributed.py	18.86% <ø> (+4.94%)	⬆️
python/cudf/cudf/core/_base_index.py	82.20% <43.75%> (-3.35%)	⬇️
python/strings_udf/strings_udf/__init__.py	86.27% <76.00%> (-10.61%)	⬇️
python/cudf/cudf/core/index.py	92.91% <95.08%> (+0.27%)	⬆️
python/cudf/cudf/__init__.py	90.69% <100.00%> (ø)
python/cudf/cudf/core/column/categorical.py	89.34% <100.00%> (ø)
python/cudf/cudf/core/scalar.py	90.52% <100.00%> (+1.25%)	⬆️
... and 8 more

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[vuule]

@gpucibot merge