[Discover] When switching from Fields API to _source, default column is confused in context view

[majagrubic]

Kibana version:
master

Describe the bug:
When in context view of Discover and we toggle the UI setting for readFromSource and navigate back to Discover, the "old" default column is still shown (eg. _source instead of Document)

Steps to reproduce:

1. Go to Discover
2. Select an index pattern that has documents
3. Click "View surrounding documents"
4. Wait for the context view to load; observe that the default column has loaded correctly (should be Document)
5. Go to Advanced Settings > Discover
6. Toggle readFieldsFromSource
7. Go back to Discover, context view should be opened
8. Observe the default column didn't change

Expected behavior:
Default column changes based on the UI setting

Screenshots (if relevant):

Errors in browser console (if relevant):

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

Any additional context:

[elasticmachine]

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