Remove the deprecated `PublishedDandiset` / `PublishedAsset` aliases

[candleindark]

Follow-up from #419, which consolidated PublishedDandiset into Dandiset and PublishedAsset into Asset but kept the old names in dandischema/models.py as deprecated aliases so that consumers would keep importing successfully:

PublishedDandiset = Dandiset
PublishedAsset = Asset

Getting rid of them takes, in order:

• Remove the use of the aliases in the consumers, e.g. dandi-archive.
• Remove the aliases from dandischema/models.py, together with the remaining in-repo uses in to_datacite and the tests.
• Decide what becomes of the PublishedDandiset / PublishedAsset keys of SCHEMA_MAP, since publish_model_schemata resolves each key with getattr(models, class_).
• Remove the copies in models_importstab.py on the linkml-conversion branch (tracked separately in Remove the temporary Published* aliases from models_importstab.py #439).

Findings as of filing (recheck before implementing)

dandi-cli is clear. Verified at e982b3bc: it uses BareAsset, which stays, but neither deprecated alias.

dandi-archive uses both, in four places. api/views/schema.py and api/tests/test_schema.py are the two #419 called out: each builds its mapping from model.__name__, so both already collapse from four entries to two silently rather than failing.

The other two are load-bearing and fail at call time rather than at import, because they pass the name as a string:

• dandiapi/api/services/publish/__init__.py:196 — validate(..., schema_key='PublishedDandiset', json_validation=True)
• dandiapi/api/services/metadata/__init__.py:65,151 — the same with 'PublishedAsset' and 'PublishedDandiset'

validate resolves the key with getattr(models, schema_key) (dandischema/metadata.py:234 and :296), and both call sites sit on the publish path, so the breakage would surface at publication rather than at startup.

The SCHEMA_MAP question. Since #419 the published-*.json files have been byte-identical to dandiset.json and asset.json, so emitting them buys nothing, and the linkml-conversion branch has already stopped generating them on the LinkML side (7ed984e9). But SCHEMA_MAP is also the accepted schema_key vocabulary, and _get_jsonschema_validator builds a URL into a released schema version from it, so dropping the keys outright would also drop the ability to validate older published metadata under its historical key.