GH-41491: [Python] remove special methods related to buffers in python <2.6

[tacaswell]

Rationale for this change

These methods are not actually used and will be removed from Cython in an upcoming release.

Closes #41491

What changes are included in this PR?

Are these changes tested?

Trust CI

Are there any user-facing changes?

No, this code should never be actually used.

• GitHub Issue: [Python] Do not use cython special methods that exist to support a version of the buffer protocol only required for py26 #41491

[github-actions]

⚠️ GitHub issue #41491 has been automatically assigned in GitHub to PR creator.

[jorisvandenbossche]

Thanks @tacaswell !

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 7 benchmarking runs that have been run so far on merge-commit 3c67091.

There were 13 benchmark results indicating a performance regression:

• Commit Run on arm64-m6g-linux-compute at 2024-05-02 12:37:39Z
  • tpch (R) with engine=arrow, format=parquet, language=R, memory_map=False, query_id=TPCH-17, scale_factor=10
  • tpch (R) with engine=arrow, format=parquet, language=R, memory_map=False, query_id=TPCH-14, scale_factor=10
• and 11 more (see the report linked below)

The full Conbench report has more details. It also includes information about 22 possible false positives for unstable benchmarks that are known to sometimes produce them.

[tacaswell]

Gah, I was sloppy and committed stripping trailing whitespace. Bit disappointed that my contribution is not pure removal 🤣 .

[jorisvandenbossche]

Auto formatting of editors ... ;)