ssh/knownhosts: remove godoc about non-supported hashed hosts

Support for hashed hosts was added in:
https://go-review.googlesource.com/c/crypto/+/40532

Change-Id: Id18dd346d727c8bc94d0230588572e9c8ee2ccb0
Reviewed-on: https://go-review.googlesource.com/90355
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ssh/knownhosts/knownhosts.go

@@ -414,7 +414,7 @@ func (db *hostKeyDB) Read(r io.Reader, filename string) error {
 
 // New creates a host key callback from the given OpenSSH host key
 // files. The returned callback is for use in
-// ssh.ClientConfig.HostKeyCallback. Hashed hostnames are not supported.
+// ssh.ClientConfig.HostKeyCallback.
 func New(files ...string) (ssh.HostKeyCallback, error) {
 	db := newHostKeyDB()
 	for _, fn := range files {