Drop support for WorkerVersion IDs on UpdateWorkerActivity

Found while analyzing https://redmine.teklia.com/issues/11528

Two years ago, when adding support for using the same WorkerVersion multiple times in a process (https://redmine.teklia.com/issues/3383), we wanted to avoid a breaking change and allowed UpdateWorkerActivity to accept both a WorkerVersion or a WorkerRun ID in #1559 (closed). The WorkerVersion ID support is limited since it only works when you used a WorkerVersion only once in the process, so it shouldn't be relied on by newer workers.

base-worker supports this since version 0.3.4 (workers/base-worker#223 (closed)), and only archived, unmaintained workers are still using versions older than that. We can drop this entirely and simplify this endpoint.