Update to parent 18, build-helper-maven-plugin hacks around groovy no longer necessary

[jonenst]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem? NO

What kind of change does this PR introduce? code cleanup

What is the current behavior? need a hack to disable groovydoc attach

What is the new behavior (if this is a feature change)? no more hack

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [X] No

If yes, please check if the following requirements are fulfilled

• [ ] The Breaking Change or Deprecated label has been added
• [ ] The migration steps are described in the following section