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/inheritedFun.kt

@@ -0,0 +1,10 @@
+//KT-2206
+trait A {
+    fun f():Int = 239
+}
+
+class B() : A
+
+fun box() : String {
+    return if (B().f() == 239) "OK" else "fail"
+}