[Time to Visualize] Breadcrumb doesn't behave correctly when switching the dashboard.allowByValueEmbeddables flag from true to false

[stratoula]

Kibana version:
7.11

Describe the bug:
I have the dashboard.allowByValueEmbeddables flag set to true and I create a Lens chart from the dashboard. When I set the flag to false and edit the Lens viz I see the Visualize link in breadcrumb which works ok as it redirects me to the list. But when I go back to history then it redirects me to the Lens Create page.

Steps to reproduce:

1. Set the dashboard.allowByValueEmbeddables to true
2. Go to Dashboard and create a new Lens Visualization
3. Set the flag to false
4. Refresh the dashboard
5. Choose the edit Lens
6. The breadcrumb has the Visualize link
7. Click the Visualize link
8. Go back to history. I can't see my chart, I see the create a new Lens viz instead

Expected behavior:
As it is suggested here we should throw an error toast and redirect to the visualize listing page any time there is value input but by value embeddables are not allowed.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[kmartastic]

@ThomThomson -- can you estimate a loe on this?

[ThomThomson]

As Time to Visualize has been quite stable, it's seeming less and less likely that users would want to disable it. And if they did, it's even less likely that they would attempt to edit a lens which was saved by value after disabling the flag.

I think that it might be the right call to remove the feature flag entirely rather than fixing bugs based around users turning it off.

I don't think removing the flag would constitute a breaking change either, but we'll have to check telemetry to see if anyone has it turned off.

[ThomThomson]

Closing this one as the plan is to remove the flag entirely.