[core] remove root index.ts file

[spalger]

It's unclear what the purpose of this file is, but I can't find anyone using it and this file imports server and public code at the same time so it needs to be fixed for #136911. Figured I would just delete it and see what y'all think.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[TinaHeiligers]

@spalger the root index file allows import {CoreStart} from 'kibana/public', ref: #32746.

[spalger]

@TinaHeiligers kibana/public resolves to the src/core/public directory, so this file isn't important for that. Additionally, in #130483 we enforced uniform import statements and these import statements were all rewritten to @kbn/core/public then and going forward.

[TinaHeiligers]

There are still a few places where import XYZ from 'kibana/server|public' is used. We'd need to update those, especially in the docs and code snippets!

[spalger]

I can submit a PR to replace those, but like I said, these don't interact with src/core/index.ts, they import src/core/public/index.ts and src/core/server/index.ts

[TinaHeiligers]

The code snippets, example plugins and docs need to reflect this change.
Update: I'm changing this to a comment rather than an explicit change request.

[TinaHeiligers]

We need to make absolutely sure the docs and code examples/snippets are updated at the same (or very shortly after) this gets merged.
Will I get this right sometime today?

[TinaHeiligers]

Another go at a plain comment. See previous comments..

[spalger]

Alright @TinaHeiligers I updated the docs and removed support for kibana/* imports

[TinaHeiligers]

LGTM!

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