Switch to using CONFS to handle install.
- chpass is the program that implements chsh which modifies /etc/shells, so it makes sense to install with this program.
- However, one could, strictly speaking, choose not to install chpass on a system, either because it will never update the shells list, or they edit it through other means.
- Additionally, /etc/shells is read by getusershell(3) in libc, which _is_ required by some programs, in particular su(1). So it could make more sense to install this file with libc instead.