Refactor: libcrmcommon: Drop pcmk__pidfile_matches()

Simplify it by using GLib, and move its body to its sole caller.

We lose the "sleep(2)" from read_pidfile(). However, the odds of this
check happening between the time the pidfile is created and when about
eight bytes have been written to the pidfile, should be minimal.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>