MINOR: [C++][Parquet] Fix *_write_page_index and set_size_statistics_level comments

[chegoryu]

Rationale for this change

Defaults were changed in this commit 1fcc892

What changes are included in this PR?

Fixed comments about default values of some writer properties

Are these changes tested?

No need to test

Are there any user-facing changes?

No

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[wgtmac]

Could you fix the lint error?

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit 0879f5b.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 3 possible false positives for unstable benchmarks that are known to sometimes produce them.