Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/traits/finalMethod.kt

@@ -0,0 +1,9 @@
+//KT-2382
+
+trait T {
+    final fun foo() = "OK"
+}
+
+class S : T { }
+
+fun box(): String = S().foo()