remove logic to handle "magic" client-side indentation

[martinlippert]

As part of #1153, we already disabled the workarounds for specific client-side magic indentation, since we configure completion items now with a InsertTextModeof As-Is, which causes the client to not apply its own logic to add indentation.

This issue here is to cleanup the unused code and logic around this, specially inside VscodeCompletionEngineAdapter

[martinlippert]

Done, cleanup work finished with 029cc73