remove the now gone -all switch from flushtree
remove the now gone -all switch from flushtree

This is for RT ticket #36832.
While here update manual page date.

each/bind9-collab,pecharmin/bind9,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab,pecharmin/bind9