[Discover] Selected fields persist even after changing index pattern

[mbondyra]

I am not exactly sure if it's a bug, @kertal can you assess?

Kibana version:
master

Steps to reproduce:

1. Use kibana instance with at least 2 index patterns defined
2. Go to discover
3. Choose some of the fields from available fields list to add them to selected fields
4. Change index pattern
5. Current behavior: the selected fields list is empty on the fields list, but the table displays them without data

Here's the video showing the behaviour: https://www.loom.com/share/20afb40eb85a497e8e12ef2ff0ddb842

Expected behavior:
Table is displayed with '_source'. (?)

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:

[lizozom]

I suspect this might be related to a use case where the same fields are present in both IPs (for example if they are using the Elastic Common Schema).

I think the better logic would be, if the field does not exist in the new IP, remove it.

[mbondyra]

Closing as it's the duplicate of #57322