How can i delete addons that i downloaded when joining server?

I have been playing on some different servers and i downloaded a lot of crap
Actually it is not a problem for me but last one downloaded a rain addon that i cant turn rain off
How do i delete these addons? they are not in my addons list
thanks

C:\Program Files (x86)\Steam\steamapps<username>\garrysmod\garrysmod\addons

Delete whichever is relevant.