SI-6964 Remove build managers, both simple and refined.

Deprecated in 2.10.0, out to pasture in 2.11.0.

Users are advised to migrate to:

   https://github.com/typesafehub/zinc
   http://www.scala-sbt.org/
Merge pull request #1897 from retronym/ticket/6964

SI-6964 Remove build managers, both simple and refined.