Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/functions/kt1649_2.kt

@@ -0,0 +1,18 @@
+trait A {
+    val method : () -> Unit?
+}
+
+fun test(a : A) {
+    if (a.method != null) {
+        a.method!!()
+    }
+}
+
+class B : A {
+    override val method = { }
+}
+
+fun box(): String {
+    test(B())
+    return "OK"
+}