How do I remove a repository from the terminal?

You would need to locate the specific lines in /etc/apt/sources.list

Open the sources file with some editor while using sudo, such as vim (I personally use nano, but you can use whatever you want):

sudo vim /etc/apt/sources.list

Locate the lines which contain the broken link, and remove them. Save the files, then run sudo apt-get update after you save the file and close out the editor. Your sources will be updated to work with the non-broken repositories.

If you need to manage PPAs then this question is for you:

• How can PPAs be removed?