Yes, that's the code from
here.
The registry key is still there, but I doubt if it has any use anymore.
Your recent blocks are now stored 'in the cloud'. So they are attached to your AutodeskID (Blocks are only accessible across devices if you use cloud storage).
On the recent tab there is a button for OPTIONS. On that panel you can turn off cloud storage.
On that same panel is the information where your recent blocks are locally stored:
In that folder there is a subfolder 'RecentBlocks'. Delete that subfolder and your recent blocks will be gone (in the next drawing).
The there is this variable BLOCKMRULIST. The initial value is 50, but you could set that value to 12.