Re-enable EditorPickCache vertex data cache #298

See in EditorPickCache.cpp:

#if 0 // TEMP: Disabling for now as we figure out dropping data at end of all read scopes

Needs to be looked at again. We are no longer dropping AssetObject blob data on UnpageBlobData(), instead we assume any non-Transient data is put into the asset registry which caches the data on disk, and trip an assert otherwise.
So this should be safe to enable.