Remove the WORKER_VERSION_ID environment variable from processes

The WORKER_VERSION_ID variable is set in training, workers and dataset processes, but so is ARKINDEX_WORKER_RUN_ID, which should be used instead.

code.vpn's index is currently very outdated, to the point where it is unable to find the files it indexed on most repos, so I can't say whether this variable is used. I found at least one use in the ABBYY importer.