C++ refactoring: Don't let ak.to_list act on v2 arrays (finishing #1201).

[jpivarski]

No description provided.

[codecov]

Codecov Report

Merging #1203 (2c54cc8) into main (1751ffc) will increase coverage by 0.00%.
The diff coverage is 55.26%.

Impacted Files	Coverage Δ
.../awkward/_v2/operations/structure/ak_singletons.py	80.00% <ø> (ø)
src/awkward/_v2/operations/convert/ak_to_list.py	50.00% <42.30%> (-30.00%)	⬇️
src/awkward/_v2/highlevel.py	64.79% <66.66%> (+0.02%)	⬆️
src/awkward/_v2/_connect/pyarrow.py	83.28% <100.00%> (-0.05%)	⬇️
src/awkward/_v2/_util.py	82.08% <100.00%> (+0.18%)	⬆️
src/awkward/_v2/contents/content.py	83.19% <100.00%> (ø)
src/awkward/_v2/contents/unionarray.py	83.40% <0.00%> (+2.00%)	⬆️