The reason the reviews are in your inbox is because you need to review them or you will forget them. Such a script would harm your learning.
I would advise you to limit your new items instead of forgetting old items. This way your inbox will be more manageable, and you’ll keep your knowledge, which is the whole point of the SRS system. This script does that, but has been superceded by valeths “Lesson Cap” script, which I suggest you use instead of this script.
Related to this: This script will stop working when WK changes their infrastructure the 18th of April., so please everyone, replace your script with Valeths script linked above. 