Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/enum/inFunction.kt

@@ -0,0 +1,11 @@
+// KT-2948 Assertion fails on a local enum
+
+fun foo(): String {
+   enum class E {
+       OK
+   }
+
+   return E.OK.toString()
+}
+
+fun box(): String = foo()