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/kt2711.kt

@@ -0,0 +1,15 @@
+class IntRange {
+    fun contains(a: Int) = (1..2).contains(a)
+}
+
+class C() {
+    fun rangeTo(i: Int) = IntRange()
+}
+
+
+fun box(): String {
+    if (2 in C()..2) {
+        2 == 2
+    }
+    return "OK"
+}