Remove dependency on Microsoft.Experimental.Collections

[bamarsha]

This dependency:

https://github.com/microsoft/qsharp-compiler/blob/73429cd30b77e3ffff96a26f36f1f3ce97236c66/src/QsCompiler/SyntaxProcessor/SyntaxProcessor.fsproj#L39

causes issues with downstream documentation publishing because all versions of Microsoft.Experimental.Collections are tagged as prerelease. It's easier to remove this dependency than to update the docs publishing scripts.