[Discover] Removes old index columns when switching index pattern

[AlonaNadler]

Requested by a users
Along the lines of user-friendliness, I noticed that whenever I change indices in the discover tab, it keeps columns from the last index I was viewing, even if those don’t exist in the new index (and in my use cases, they often don’t).
I realize the user can explicitly select “save” and “save as new search” and then later go to “open” and select the view they wanted, however to me it seems like we’re

1. just asking the user to do more unnecessary work and
2. this IMO affects user perception of “polish” (I don’t think it looks very good when we display dead columns) and user-friendliness.

My personal suggestion would be to

1. just remove any columns from the view that don’t exist in the new index and
2. show whatever columns were viewed for that index last time (preferably by that user, but to my knowledge kibana doesn’t have a 1st-party cookie - maybe this is a good example of why we might want to consider one), but of course anything along these lines would be helpful.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[kertal]

Add-on: Also columns selected to sorted by, that don't exist in the new index pattern should be removed from sorting