Suggestion: `no-redundant-key`

[SimonSchick]

I noticed that after refactorings we sometimes forgot to remove the key on the root fragment of a new component, this seems to be entirely redundant and just add overhead.

example:

const Component: FC = () => {
          // v key is redundant here
   return <p key={1}>test</test>;
}

This would be effectively the counter-rule to `https://github.com/jsx-eslint/eslint-plugin-react/blob/master/docs/rules/jsx-key

I think a good heuristic would be to match any fragment that is not contained within a callback eg. Array.map.

[ljharb]

key does serve a purpose, even outside a list - in other words, it's not redundant. See https://kentcdodds.com/blog/understanding-reacts-key-prop

What this means is that I'm not sure there's any way to statically identify a key prop that should be removed, since potentially all of them could be meaningful.