Drop defn.SingletonType

Risk of confusing with Types.SingletonType is too high.

Author: odersky

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -357,7 +357,6 @@ class Definitions {
     enterCompleteClassSymbol(
       ScalaPackageClass, tpnme.Singleton, PureInterfaceCreationFlags | Final,
       List(AnyClass.typeRef), EmptyScope)
-  def SingletonType = SingletonClass.typeRef
 
   lazy val SeqType: TypeRef = ctx.requiredClassRef("scala.collection.Seq")
   def SeqClass(implicit ctx: Context) = SeqType.symbol.asClass

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -404,7 +404,7 @@ object ProtoTypes {
   /** Create a new TypeVar that represents a dependent method parameter singleton */
   def newDepTypeVar(tp: Type)(implicit ctx: Context): TypeVar = {
     val poly = PolyType(DepParamName.fresh().toTypeName :: Nil)(
-        pt => TypeBounds.upper(AndType(tp, defn.SingletonType)) :: Nil,
+        pt => TypeBounds.upper(AndType(tp, defn.SingletonClass.typeRef)) :: Nil,
         pt => defn.AnyType)
     constrained(poly, untpd.EmptyTree, alwaysAddTypeVars = true)
       ._2.head.tpe.asInstanceOf[TypeVar]