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?