system/skeleton: drop shutdown user from shadow

It has no counterpart in passwd so it's basically a NOP.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

system/skeleton/etc/shadow

@@ -3,7 +3,6 @@ bin:*:10933:0:99999:7:::
 daemon:*:10933:0:99999:7:::
 lp:*:10933:0:99999:7:::
 sync:*:10933:0:99999:7:::
-shutdown:*:10933:0:99999:7:::
 halt:*:10933:0:99999:7:::
 uucp:*:10933:0:99999:7:::
 operator:*:10933:0:99999:7:::