Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/controlStructures/kt299.kt

@@ -0,0 +1,17 @@
+class MyRange1() : Range<Int> {
+    override fun contains(item: Int) = true
+}
+
+class MyRange2() {
+    fun contains(item: Int) = true
+}
+
+fun box(): String {
+    if (1 in MyRange1()) {
+        if (1 in MyRange2()) {
+            return "OK"
+        }
+        return "fail 2"
+    }
+    return "fail 1"
+}