When a new runtime removes an event variant, we can no longer reference it in the query-node/hydra manifest.yml as the metadata for the event runtime type is not found in the latest runtime. But we need to keep the mapping to handle the event when it was emitted in previous runtimes. (This is because we currently have a single set of mappings that need to work all the way from genesis)

Keeping around unused runtime types in the runtime is not ideal.

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