[CPP/Doc] Remove outdated Parquet documentation

[asfimport]

Instructions documented in https://github.com/apache/arrow/blob/master/cpp/doc/Parquet.md are not valid anymore.

Reporter: Krisztian Szucs / @kszucs
Assignee: Krisztian Szucs / @kszucs

PRs and other links:

• GitHub Pull Request #3516

_{Note: This issue was originally created as ARROW-4408. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 3516
#3516