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/kt2532.kt

@@ -0,0 +1,15 @@
+package foo
+
+trait B {
+    val c: Int
+        get() = 2
+}
+
+class A(val b: B) : B by b {
+    override val c: Int = 3
+}
+
+fun box(): String {
+    val c = A(object: B {}).c
+    return if (c == 3) "OK" else "fail: $c"
+}