udev: set fewer process properties

On systemd systems we generally don't need to chdir() to root, we don't
need to setup /dev/ ourselves (as PID 1 does that during earliest boot),
and we don't need to set the OOM adjustment values, as that's done via
unit files.

Hence, drop this. if people want to use udev from other init systems
they should do this on their own, I am very sure it's a good thing to do
it from outside of udevd, so that fewer privileges are required by udevd. In
particular the dev_setup() stuff is something that people who build
their own non-systemd distros want to set up themselves anyway, in
particular as they already have to mount devtmpfs themselves anyway.

Note that this only drops stuff that isn't really necessary for testing
stuff, i.e. process properties and settings that don't matter if you
quickly want to invoke udev from a terminal session to test something.

src/udev/udevd.c

@@ -1859,10 +1859,6 @@ int run_udevd(int argc, char *argv[]) {
         }
 
         /* set umask before creating any file/directory */
-        r = chdir("/");
-        if (r < 0)
-                return log_error_errno(errno, "Failed to change dir to '/': %m");
-
         umask(022);
 
         r = mac_selinux_init();
@@ -1873,8 +1869,6 @@ int run_udevd(int argc, char *argv[]) {
         if (r < 0 && r != -EEXIST)
                 return log_error_errno(r, "Failed to create /run/udev: %m");
 
-        dev_setup(NULL, UID_INVALID, GID_INVALID);
-
         if (getppid() == 1 && sd_booted() > 0) {
                 /* Get our own cgroup, we regularly kill everything udev has left behind.
                  * We only do this on systemd systems, and only if we are directly spawned
@@ -1917,10 +1911,6 @@ int run_udevd(int argc, char *argv[]) {
 
                 /* child */
                 (void) setsid();
-
-                r = set_oom_score_adjust(-1000);
-                if (r < 0)
-                        log_debug_errno(r, "Failed to adjust OOM score, ignoring: %m");
         }
 
         return main_loop(manager);