Remove notebook controller kind API proposal

[mjbvz]

Fixes #168535

[rebornix]

Thanks @mjbvz, we also need to remove notebookControllerKind from the Jupyter extension, not sure if the Jupyter extension needs to be updated first.

[mjbvz]

I reviewed the jupyter code. Looks like there are two places where we use kind:

• Setting the kind: https://github.com/microsoft/vscode-jupyter/blob/8e55e3617f1f0f21524aef018abe62879e66be95/src/notebooks/controllers/vscodeNotebookController.ts#L318

• Showing a kernel picker: https://github.com/microsoft/vscode-jupyter/blob/e1152ca1329bc7dfb264dfdc19acd41073aef89d/src/notebooks/controllers/commands/serverConnectionControllerCommands.ts#L195

I think both should still work after this PR

@DonJayamanne Can you please take a look and confirm that we are good to remove the kind property?

[DonJayamanne]

Lets merge this PR once we have removed this in Jupyter extension microsoft/vscode-jupyter#13068

[mjbvz]

Should be good to merge now that we've removed the flat kernel picker