gnt-network(8): Remove "rename"

It is not implemented after all.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

man/gnt-network.rst

@@ -115,13 +115,6 @@ LIST-FIELDS
 
 List available fields for networks.
 
-RENAME
-~~~~~~
-
-| **rename** {*oldname*} {*newname*}
-
-Renames a given network from *oldname* to *newname*. NOT implemeted yet
-
 TAGS
 ~~~