xuser-account: remove GROUPADD_PARAM

The group shutdown had been provided by base-passwd, otherwise, it may cause
sysvinit failed to build:

$ bitbake xuser-account sysvinit && bitbake xuser-account sysvinit -ccleansstate && bitbake sysvinit
[snip]
| chown: invalid user: root.shutdown
[snip]

(From OE-Core rev: d72793ca3cbedca3eaca2a7c62f4c93d3c3af358)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/user-creation/xuser-account_0.1.bb

@@ -21,7 +21,6 @@ do_install() {
 FILES_${PN} = "${sysconfdir}/dbus-1/system.d/system-xuser.conf"
 
 USERADD_PACKAGES = "${PN}"
-GROUPADD_PARAM_${PN} = "--system shutdown"
 USERADD_PARAM_${PN} = "--create-home \
                        --groups video,tty,audio,input,shutdown,disk \
                        --user-group xuser"