gutenberg_warn_classic_about_blocks: tedious dialog with only one working option!

[bobbingwide]

Describe the bug
When using the Classic editor to edit a post that contains Gutenberg blocks the warning dialog is
very annoying after Update, especially since the only button that works is the Continue to Classic editor button.

To Reproduce
Steps to reproduce the behavior:

1. Activate Gutenberg and the Classic editor
2. List posts
3. Choose Classic Editor to edit a post created using Gutenberg. e.g. Hello World!
4. See the warning dialog
5. Click on Edit in Gutenberg
6. See the warning dialog
7. Click on Continue to Classic Editor
8. Update
9. See the warning dialog.
10. Go to 5.

Expected behavior

• The dialog should only appear for the first attempt to edit the post.
• The Edit in Gutenberg button should work.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Edge, in this example, but problem noted on Safari on iPad
• Version [e.g. 22]

Additional context

• WordPress 5.0-beta4 used to create the Hello World post
• Classic editor 0.5
• Gutenberg 4.1.0 and above.
• Note: 4.0.0 doesn't work with 5.0-beta4

[bobbingwide]

The steps to reproduce is now different due to changes to the Classic Editor plugin. Users of Classic Editor v0.5 will need to update to v1.3 or higher.

• The site admin will have to enable switching of editors and set a default editor.
• Each user who wants to use the switch editor capability may edit their User profile to choose a default editor.
• Editor switching can be done per post; once the editor has been loaded, or from the posts list.
• The dialog is shown when you switch to Classic
• If the post contains blocks it still gets displayed every time
• And choosing Block editor still doesn’t work.

[bobbingwide]

The workaround is to deactivate Gutenberg.

[gziolo]

gutenberg_warn_classic_about_blocks is no longer part of Gutenberg plugin. See related PR: #13442.