Deprecate CompletionItem.deprecated

[KamasamaK]

In v3.15, CompletionItem.tags was added which can tag a completion item as deprecated, so the dedicated deprecated property is now redundant.

[dbaeumer]

The property is already deprecated in the latest next build

	 * @deprecated Use `tags` instead.

[KamasamaK]

Thanks. I couldn't (and still can't) find that anywhere in this repository.

[dbaeumer]

https://github.com/Microsoft/vscode-languageserver-node/blob/master/types/src/main.ts#L1469

[KamasamaK]

I see. I was referring to the LSP spec, not the VS Code SDK.