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/

(Not much) discussion: https://groups.google.com/d/topic/scala-internals/QiheDz46nG8/discussion

Let's see if we get a bit more as a pull request.

Review by @paulp @dragos (for the IDE)