Remove deprecated output property in Node.js API result object

[ybiquitous]

When releasing 16.0.0, we announced we would remove the output property in the Node.js API result object in the next major version. See the migration guide and code:

stylelint/docs/migration-guide/to-16.md

Line 263 in da7ce21

We've deprecated the [`output`](../user-guide/node-api.md#output) property in favor of the new `report` and `code` ones, and we'll remove it in the next major version.

stylelint/lib/prepareReturnValue.mjs

Lines 45 to 53 in da7ce21

	// TODO: Deprecated. Remove in the next major version.
	get output() {
	if (!this._outputWarned) {
	console.warn('`output` is deprecated. Use `report` or `code` instead.');
	this._outputWarned = true;
	}
	return this._output ?? '';
	},