ngctl.8: fix incorrect synopsis

Tiny manpage bug I caused in D50241
I left a line in the manpage that shouldn't be there.

MFC after:	3 days
Fixes:		72d01e62b0 ("netgraph: teach ngctl to attach and run itself in a jail")
Reviewed by:	des, markj
Differential Revision:	https://reviews.freebsd.org/D55485

usr.sbin/ngctl/ngctl.8

@@ -44,7 +44,6 @@
 .Op Fl f Ar filename
 .Op Fl n Ar nodename
 .Op Ar command Op Ns Ar argument ...
-.Op Ar command ...
 .Sh DESCRIPTION
 The
 .Nm