Pack zuul git refs daily.

Zuul was packing git refs weekly, do this daily instead to handle the
number of refs created by gate resets in large gate queues.

Change-Id: I8fc8c78436ebf79b457d392f1ce8de31b15c762c

modules/zuul/manifests/init.pp

@@ -225,7 +225,6 @@ class zuul (
 
   cron { 'zuul_repack':
     user        => 'zuul',
-    weekday     => '0',
     hour        => '4',
     minute      => '7',
     command     => 'find /var/lib/zuul/git/ -maxdepth 3 -type d -name ".git" -exec git --git-dir="{}" pack-refs --all \;',