Where does Homebrew store its installed packages list?
If I understood correctly, here is the list of the folder HomeBrew creates while installing it on your machine. 



Homebrew installs packages to their own directory and then symlinks their files into /usr/local.

And when you do brew list, it shows the tool that you get from it under Cellar Folder. So you can check all this folder to get rid of it properly. 

For example, if I install wget as "brew install wget" then when I run brew list, it shows me as