Remove deprecated api method FileContents::inPackageInfo from code

deprecafed in 10.2 (april 2022) https://github.com/checkstyle/checkstyle/commit/f6a15cfb3c3c64d16c269bd8240722c7f9d7974e#diff-0910ced16436543c1477e7a3528483b46612a86971ff771893e89700f85dfb3dR335

deprecation issue - https://github.com/checkstyle/checkstyle/issues/11507

We need to find some major version update time, and remove such methods from our API.
We need to recheck plugins(maven, eclipse-cs, sonar, ...... gradle, idea.....) if they need to be updated or notify/help them to upgrade.

issue is created based on conversation :
https://github.com/checkstyle/checkstyle/pull/11639

Start with FileContents::inPackageInfo and the deprecation commit linked in the issue, then read issue #11507 and pull request #11639 for the surrounding context. Check the Maven, Eclipse CS, Sonar, Gradle, and IDEA plugin integrations mentioned in the issue; done means the deprecated method is removed and affected plugins are rechecked or notified.

Written by the indexing model from the issue text.