how to unstall the sims4 holiday celebration

It seems you can just delete the folder with the files in.

It's called FP01 and should be in your Sims 4 installation folder (usually programs(x86)\Origin_Games 

Here's a conversation I had about it: https://twitter.com/crinrict/status/547678985447288832

You'll be trying at your own risk. Backup your user files: http://sims4.crinrict.com/en/2014/09/backups/