cubicweb #3007241 drop ETYPE_NAME_MAP [open]

this is an attempt to support renaming of entity types while rql and other things (eg schema lookup) using the old entity types would still work.

While this is somewhat working, this is undocumented, has many fallbacks and introduce complexity. We should probably not support this at all.

NB: rename_entity migration primitive seems to rely on this for type merging (ie renaming an entity type to an already existing entity type). It would be nice to keep this though.

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