Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/closures/recursiveClosure.kt

@@ -0,0 +1,7 @@
+fun foo(s: String): String {
+    fun bar(count: Int): String =
+        if (count == 0) s else bar(count - 1)
+    return bar(10)
+}
+
+fun box(): String = foo("OK")