[Discover] Remove legacy/classic table

[davismcphee]

In version 9.0, we are removing the legacy/classic table in Discover.

The following needs to be done:

• Remove the doc_table:legacy setting from the Discover app and all associated code related to the legacy table view.
• Remove the truncate:maxHeight setting since it is only relevant to the legacy table.
• Remove all the code + tests depending on these settings

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

The legacy table doesn't use virtualization when rendering table rows, instead rendering them all at once, which has the side effect of supporting local filtering through built in find functionality in browsers. Unified Data Table is based on EuiDataGrid, which uses virtualization and prevents relying on browser find functionality for local filtering. In order to support this we'd need to implement in-app filtering in Unified Data Table.

About the legacy in-app filtering... it depends, because it renders the list in chunks when scrolling. So when you scroll down you can use the browser to find in all results displayed. Apart from that detail, yes, we should implement searching in the results #70799

[davismcphee]

@kertal thanks for the clarification! Updated the bullet to include that info.

[jughosta]

And we could remove truncate:maxHeight

[kertal]

I rewrote this issue to describe the task that needs to be done, we just need to decide when it's the right time, to omit backports of other issues that follow this merge, won't run into too much conflicts