Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/properties/kt1714_minimal.kt

@@ -0,0 +1,12 @@
+trait A {
+    val v: Int
+}
+
+class AImpl : A {
+    override val v: Int = 5
+}
+
+public fun box() : String {
+    (AImpl() : A).v
+    return "OK"
+}