As of Scala 2.13, Unicode arrows are deprecated:
* https://github.com/scala/scala/pull/7540
* https://github.com/scala/scala-dev/issues/585
* https://github.com/scala/bug/issues/11210
Using one will give a deprecation warnings like so:
> The unicode arrow `⇒` is deprecated, use `=>` instead. If you still wish to
> display it as one character, consider using a font with programming ligatures
> such as Fira Code.
As such the Scala layer's version slick capability to replace ASCII arrows with
Unicode ones is no longer useful, and I have removed it.
Based on my tests it doesn't seem that there is a need for a more graceful way
to deprecate this: i.e. nothing fails if there is extra junk in `:variables`.