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/delegationJava.kt

@@ -0,0 +1,13 @@
+class TestJava(r : Runnable) : Runnable by r {}
+class TestRunnable() : Runnable {
+  public override fun run() = System.out.println("foobar")
+}
+
+fun box() : String {
+    var del = TestJava(TestRunnable())
+    del.run()
+    if (del !is Runnable)
+        return "Fail #1"
+
+    return "OK"
+}