Rollup merge of #124266 - RalfJung:no-answer, r=joboet

remove an unused type from the reentrant lock tests

At least it seems unused. This was added back in 45aa6c8d1bc2f7863c92da6643de4642bb2d83bf together with a test related to poisoning; when the test got removed, it seems like it was forgotten to also remove this type.

Author: matthiaskrgr