Don't generate generic signature for local classes

Author: Duhemm

compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala

@@ -500,7 +500,8 @@ object GenericSignatures {
           case PolyType(_, _) =>
             true
           case ClassInfo(_, _, parents, _, _) =>
-            foldOver(tp.typeParams.nonEmpty, parents)
+            // Local classes don't need a signature
+            !tp.classSymbol.owner.is(Method) && foldOver(tp.typeParams.nonEmpty, parents)
           case AnnotatedType(tpe, _) =>
             foldOver(x, tpe)
           case proxy: TypeProxy =>