Remove Java Flight Recorder

[koppor]

This removes Java Flight Recorder

Java Flight Recorder requires a commercial license for use in production.
[...]
Java Flight Recorder (JFR) is a tool for collecting diagnostic and profiling data about a running Java application.

I think, we never used it on a user's side, so would remove it for our distribution.

On a case-per-case-basis, we (or some researchers) could include jdk.jfr back locally.

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[Siedlerchr]

I thought the open jdk version is free to use

[koppor]

I thought the open jdk version is free to use

In case you have source for that? Maybe, its the client tooling accessing the JFR data. I don't use profiling tooling in my daily work with JabRef. I perceived that we as group do profiling "on demand" when we concentrate on memory consumption etc. For this case, we are free to re-use any module required to do that. - However, in 99,99% of the usages of JabRef, the modules is NOT used. Furthermore, using the module prevents us to switch to other JDKs. Not OpenJ9 and IMHO also not GraalVM. Further, removing the module makes the distrubtion size smaller and gains a (small) bit of performance.