rgw: remove rgw_realm_reconfigure_delay

rgw: remove rgw_realm_reconfigure_delay

when the master zone is changed, this config variable was increasing the
window of time where the old master zone would continue to handle
requests to modify metadata. those changes would not be reflected by the
new metadata master zone, and would be lost to the cluster

it was an attempt to optimize for the unlikely case of multiple period
changes in a short period of time, but the logic in reload() handles this
case correctly as is

Signed-off-by: Casey Bodley <cbodley@redhat.com>