Pick up latest markdown language service and clean up server package (#164516)

- Picks up newest markdown language service
- Excludes some files from server publish
- Delete unused file
- Update readme
- Align server version with LS version

extensions/markdown-language-features/server/src/util/arrays.ts

@@ -1,11 +0,0 @@
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-
-/**
- * @returns New array with all falsy values removed. The original array IS NOT modified.
- */
-export function coalesce<T>(array: ReadonlyArray<T | undefined | null>): T[] {
-	return <T[]>array.filter(e => !!e);
-}