Drop ProjectReference implicit lifts

main-settings/src/main/scala/sbt/Reference.scala

@@ -94,13 +94,4 @@ object Reference {
     case BuildRef(b)      => Some(b)
     case _                => None
   }
-
-  @deprecated("Explicitly wrap the URI in a call to RootProject.", "0.13.0")
-  implicit def uriToRef(u: URI): ProjectReference = RootProject(u)
-
-  @deprecated("Explicitly wrap the File in a call to RootProject.", "0.13.0")
-  implicit def fileToRef(f: File): ProjectReference = RootProject(f)
-
-  @deprecated("Explicitly wrap the String in a call to LocalProject.", "0.13.0")
-  implicit def stringToReference(s: String): ProjectReference = LocalProject(s)
 }

sbt/src/sbt-test/compiler-project/src-dep-plugin/build.sbt

@@ -1,5 +1,5 @@
 import Configurations.{CompilerPlugin => CPlugin}
 
-lazy val use = project.dependsOn(file("def") % CPlugin).settings(
+lazy val use = project.dependsOn(RootProject(file("def")) % CPlugin).settings(
 	autoCompilerPlugins := true
 )

sbt/src/sbt-test/project/src-plugins/project/p.sbt

@@ -1,2 +1,2 @@
 lazy val root = (project in file(".")).
-  dependsOn(file("../plugin"))
+  dependsOn(RootProject(file("../plugin")))