Revert "Upgrade parent pom version from 31 to 33"

[vinishjail97]

This reverts commit fc262c0.

Important Read

• Please ensure the GitHub issue is mentioned at the beginning of the PR

What is the purpose of the pull request

#486
mvn deploy -Prelease -DskipTests -DdeployArtifacts=true is failing for version 33 as it's not supporting java 1.8 docs.
Looked up other OSS projects and official documentation we can use any version greater than 22. https://maven.apache.org/pom/asf/

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.8.0:jar (attach-javadocs) on project xtable-api: MavenReportException: Error while generating Javadoc: 
[ERROR] Exit code: 1
[ERROR] /Users/vinishreddy/helm/configs/incubator-xtable/xtable-api/target/delombok/org/apache/xtable/spi/extractor/ExtractFromSource.java:38: error: method references are not supported in -source 7
[ERROR]     Iterator<TableChange> tableChangeIterator = commitsBacklog.getCommitsToProcess().stream().map(conversionSource::getTableChangeForCommit).iterator();
[ERROR]                                                                                                                     ^
[ERROR]   (use -source 8 or higher to enable method references)
[ERROR] /Users/vinishreddy/helm/configs/incubator-xtable/xtable-api/target/delombok/org/apache/xtable/spi/sync/TableFormatSync.java:64: error: lambda expressions are not supported in -source 7
[ERROR]         results.put(conversionTarget.getTableFormat(), getSyncResult(conversionTarget, SyncMode.FULL, internalTable, target -> target.syncFilesForSnapshot(snapshot.getPartitionedDataFiles()), startTime, snapshot.getPendingCommits()));

Brief change log

(for example:)

• Revert back apache parent pom version to 31 as mvn deploy is failing

Verify this pull request

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This pull request is a trivial rework / code cleanup without any test coverage.

[zabetak]

A plain revert may mess up again the distribution years in the NOTICE file inside the jars. I have an idea that can fix the problem without a full revert; will create a PR shortly.

[zabetak]

@vinishjail97 Please check #517 and let me know your thoughts.