To remove a user from a team library, click on the team library in the sidebar and press the red Invite button. From the library sharing dialog, find the user you wish to remove from the team member list. Then press the down arrow to the right of their name and select Remove.
Removing them from a team library will immediately revoke their access to the team library and all it's contained notebooks and notes. If the user has authored any notes within a team library, they'll still be listed as an author of the note. But they will no longer have access to it.