The last 2.x version before 3.0 is a great time to flag things we might want to get rid of for good on 3.0.

In terms of actions, I did a quick pass and here are potential candidates:

• relationships_*: This has came up regularly, there is demand for the feature but the current implementation is broken or has unknown status (see Fix, document and rewrite tests for dataset relationships (or remove) #4212, Package relationships UI visualization #5273). An extension with a new fresh implementation seems like the best approach (see e.g. Dataset relations POC ckanext-dcat#335)
• vocabulary_* +, tag_*: Again, something potentially useful but with an undocumented and limited implementation (e.g. I don't think it supports multilingual tags, no UI for vocabularies etc).
• resource_search: this uses db queries which makes me nervous, we should review it
• term_translation_*: not sure what these are used for

What are your thoughts on these ones?
Can you think of any other candidate for deprecation?