reverted fixes for FILEUPLOAD-293

[StefanSpieker]

reverted fixes for FILEUPLOAD-293 since this was fixed in Commons-FileUpload 1.5

I'm not sure if it should be a changlog entry or not.

Testing done

I verified that after removing the fix, following isue couldn't be reproduced: JENKINS-65327

Proposed changelog entries

• removed fixes after available in upstream Commons Fileupload

Proposed upgrade guidelines

N/A

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@mention

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[MarkEWaite]

I've confirmed that I can see the test failures consistently on my RHEL 8 with Java 11 when using this pull request, but don't see those failures when I run the same command from the master branch. The command that I run is:

mvn -Dtest=PluginManagerTest clean verify

[StefanSpieker]

Thanks @MarkEWaite