Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/classes/kt2390.kt

@@ -0,0 +1,35 @@
+
+class JsonObject() {
+}
+
+class JsonArray() {
+}
+
+public trait Formatter<in IN: Any, out OUT: Any> {
+    public fun format(source: IN?): OUT
+}
+
+public trait MultiFormatter <in IN: Any, out OUT: Any> {
+    public fun format(source: Collection<IN>): OUT
+}
+
+public class Project() {
+}
+
+public trait JsonFormatter<in IN: Any>: Formatter<IN, JsonObject>, MultiFormatter<IN, JsonArray> {
+    public override fun format(source: Collection<IN>): JsonArray {
+        return JsonArray();
+    }
+}
+
+public class ProjectJsonFormatter(): JsonFormatter<Project> {
+   public override fun format(source: Project?): JsonObject {
+        return JsonObject()
+    }
+}
+
+
+fun box(): String {
+  val formatter = ProjectJsonFormatter()
+  return if (formatter.format(Project()) != null) "OK" else "fail"
+}