fix(nextclade): align dataset metadata with schema

[ivan-aksamentov]

Remove obsolete top-level metadata fields from all 4 Nextclade dataset configs.

These fields are not defined in the pathogen.json schema and are silently ignored by Nextclade. The enabled and official fields do not exist in the schema at all. The deprecated and experimental flags belong under attributes but are both false (the default), so they are removed rather than moved.

Field	Action	Datasets
deprecated: false	Remove (default is false)	all-clades, clade-i, clade-iib, lineage-b.1
experimental: false	Remove (default is false)	all-clades, clade-i, clade-iib, lineage-b.1
enabled: true	Remove (not in schema)	all-clades, clade-i, clade-iib, lineage-b.1
official: true	Remove (not in schema)	all-clades, clade-i, clade-iib, lineage-b.1

• Remove deprecated, experimental, enabled, official from 4 dataset configs

⚠️ The existing datasets in nextclade_data are already patched in nextstrain/nextclade_data#436, so no immediate resubmission is needed. But without this upstream fix, the obsolete fields will reappear on the next dataset submission from this workflow.

ℹ️ See pathogen.json schema for the PathogenJson definition.

1. Related to: fix: update mpox dataset schema fields nextclade_data#436