How to remove old entries from known_hosts?

[Chris Green]

Is there any way to remove old entries from the known_hosts file? With
the hashed 'names' one can't easily see which entries are which.  I
have around 150 lines in my known hosts but in reality I only ssh to a
dozen or so systems.  All the redundant ones are because I have a
mixed population of Raspberry Pis and such on my LAN and they get
rebuilt fairly frequently and thus, each time, get a new entry in
known_hosts.

As a result I have to set 'PreferredAuthentications password' for some
systems because there are *loads* of redundant keys which cause login
to fail otherwise.

-- 
Chris Green