Remove Scala guides

We no longer write Scala on a regular basis. This guide has not been
touched in years. Let's sunset it.

Author: JoelQ

README.md

@@ -53,7 +53,6 @@ programming in style.
 - [Python](/python/)
 - [Ruby](/ruby/)
 - [Sass](/sass/)
-- [Scala](/scala/)
 - [Shell](/shell/)
 - [Swift](/swift/)