w: shows more users than `w` from procps-ng

[cakebaker]

Our implementation of w shows more users than w from procps-ng:

$ cargo run -q w
USER     TTY      LOGIN@   IDLE   JCPU   PCPU WHAT
dho      tty1     07:29    TODO   0.08   0.08 /usr/bin/startplasma-wayland
dho      pts/0    07:29    TODO   5127.583.13 /usr/bin/kded6
dho      pts/1    07:29    TODO   87.50  0.01 /bin/bash
dho      pts/2    07:32    TODO   1.95   0.05 /bin/bash
dho      pts/3    07:32    TODO   0.36   0.24 /bin/bash
dho      pts/4    07:32    TODO   0.19   0.04 /bin/bash
dho      pts/5    07:32    TODO   0.06   0.06 /bin/bash

$ w
 16:31:58 up  9:03,  2 users,  load average: 0.26, 0.24, 0.20
USER     TTY       LOGIN@   IDLE   JCPU   PCPU  WHAT
dho      tty1      07:29    9:03m  0.08s  0.08s /usr/bin/startplasma-wayland
dho                07:29    8:59m  0.00s  0.95s /usr/lib/systemd/systemd --user