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/kt1688.kt

@@ -0,0 +1,10 @@
+fun box(): String {
+    var s = ""
+    try {
+        throw RuntimeException()
+    } catch (e : RuntimeException) {
+    } finally {
+        s += "OK"
+    }
+    return s
+}