Remove --nsrun-dir option

pasta can identify a netns as a "name", which is to say a path relative to
(usually) /run/netns, which is the place that ip(8) creates persistent
network namespaces.  Alternatively a full path to a netns can be given.

The --nsrun-dir option allows the user to change the standard path where
netns names are resolved.  However, there's no real point to this, if the
user wants to override the location of the netns, they can just as easily
use the full path to specify the netns.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

passt.1

@@ -458,12 +458,6 @@ without \-\-userns.
 If the target network namespace is bound to the filesystem (that is, if PATH or
 NAME are given as target), do not exit once the network namespace is deleted.
 
-.TP
-.BR \-\-nsrun-dir " " \fIpath
-Directory for nsfs mountpoints, used as path prefix for names of namespaces.
-
-The default path is shown with --help.
-
 .TP
 .BR \-\-config-net
 Configure networking in the namespace: set up addresses and routes as configured