acct-user/bird: We can’t use birdc as shell

It’s installed by bird, so it will introduce a cyclic dependency.

Package-Manager: Portage-2.3.89, Repoman-2.3.20
Signed-off-by: Alarig Le Lay <alarig@swordarmor.fr

acct-user/bird/bird-0.ebuild

@@ -11,6 +11,5 @@ DESCRIPTION="User for BIRD"
 # TCP port 179, but 179 is already used by acct-group/_bgpd
 ACCT_USER_ID=180
 ACCT_USER_GROUPS=( bird )
-ACCT_USER_SHELL=/usr/bin/birdc
 
 acct-user_add_deps