Remove project definitions in tutorials

They get picked up by sbt when running publish, confusing the versions.
Projects are defined in the main akka project.

akka-tutorials/akka-tutorial-first/project/plugins/Plugins.scala

@@ -1,6 +0,0 @@
-import sbt._
-
-class Plugins(info: ProjectInfo) extends PluginDefinition(info) {
-  val akkaRepo   = "Akka Repo" at "http://akka.io/repository"
-  val akkaPlugin = "se.scalablesolutions.akka" % "akka-sbt-plugin" % "1.1-SNAPSHOT"
-}