Allow all permissions assigned to a user to be unassigned with one click

As a library administrator, I need to remove permissions from the record of user who no longer works at the library (but still has an active user record.)

*Use case
At the end of every semester, some of the student workers leave the employ of the library. I would like to be able to "unassign" all perms in the same modal as I assign perms."

Mockups are attached to the linked story