Revert "Fix potential race condition between evaluator and partition"

[lava]

This reverts commit 3c93213.

We empirically verified that this fixes a segfault that can occur when running an export containing a partition that is ejected from the LRU cache while the export is going on, but I don't really understand the root cause so far :'(

📔 Description

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

[tobim]

I approved the original commit. I also wonder what is wrong with it, but getting the app to work again can come before the rest of the investigation.