Add NoInits when reading a Scala2 pure interface

NoInits is implied for pure interfaces, so has to be set. The Java classfile parser
already does the right thing here.

Author: odersky

src/dotty/tools/dotc/core/unpickleScala2/PickleBuffer.scala

@@ -220,7 +220,7 @@ object PickleBuffer {
       DEFERRED_PKL -> Deferred,
       FINAL_PKL -> Final,
       METHOD_PKL -> Method,
-      INTERFACE_PKL -> PureInterface,
+      INTERFACE_PKL -> NoInitsInterface,
       MODULE_PKL -> Module,
       IMPLICIT_PKL -> Implicit,
       SEALED_PKL -> Sealed,