cubicweb-brainomics #3446604 get rid of identifier, use cwuri instead [deprecated]

While discussing with Vincent the use of identifier in Brainomics, it appeared the current situation is far from ideal:
* if required, identifier should be unique,
* identifier is currently required, but some projects do not need it.

The idea is to get rid of identifier from (most?) entities in brainomics and its direct dependencies (use cwuri instead?)

done in0.9.0
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