Remove CHANGELOG.md

[DoctorKrolic]

This is just a copy of a changelog from the extension repo, meaning it doesn't represent changes actually made to the server side. So it is just a maintance burden to keep it in sync with the extension's changelog with no clear benifits. Morover, currently even though the server is separated from the extension, they are still very much tied together and server changes are motivated only by extension's needs. My idea is to change that when the server becomes a separate thing (#33) and version it separately as well (e.g. starting from 1.0.0), but I don't think we've reached the quality bar for this yet. If that plan comes true though we will have to rewrite the changelog with the respect to new versioning anyway, so it is +1 reason to remove current changelog and not bother copying it every time we release a new extension version

[tintoy]

At one stage, the language server was also being consumed by an Eclipse extension (which is why it had its own change log) but they don’t seem to be consuming it anymore so I guess this change is fine.