Fix printing of type lambdas

The previous scheme accidentally printed <label> modifiers which ruined
the Tasty tests,

Author: odersky

src/dotty/tools/dotc/ast/tpd.scala

@@ -21,7 +21,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   private def ta(implicit ctx: Context) = ctx.typeAssigner
 
   def Modifiers(sym: Symbol)(implicit ctx: Context): Modifiers = Modifiers(
-    sym.flags & ModifierFlags,
+    sym.flags & (if (sym.isType) ModifierFlags | VarianceFlags else ModifierFlags),
     if (sym.privateWithin.exists) sym.privateWithin.asType.name else tpnme.EMPTY,
     sym.annotations map (_.tree))
 

src/dotty/tools/dotc/core/Flags.scala

@@ -437,7 +437,6 @@ object Flags {
   /** Flags representing modifiers that can appear in trees */
   final val ModifierFlags =
     SourceModifierFlags | Module | Param | Synthetic | Package | Local |
-    CovariantOrOuter | ContravariantOrLabel |
     commonFlags(Mutable)
       // | Trait is subsumed by commonFlags(Lazy) from SourceModifierFlags