Update the man page to reflect that "-M" and "-N" are deprecated and ignored.

r356242 updated nfsstat.c to report that the "-M" and "-N" options were
being ignored. These options have never had any meaning for the new NFS
code (which is now the only NFS code).
This patch updates the man page to reflect this.

This is a content change.

usr.bin/nfsstat/nfsstat.1

@@ -28,7 +28,7 @@
 .\"     From: @(#)nfsstat.1	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd December 21, 2019
+.Dd December 31, 2019
 .Dt NFSSTAT 1
 .Os
 .Sh NAME
@@ -40,8 +40,6 @@ statistics
 .Nm
 .Op Fl -libxo
 .Op Fl cdEemszW
-.Op Fl M Ar core
-.Op Fl N Ar system
 .Op Fl w Ar wait
 .Sh DESCRIPTION
 The
@@ -94,17 +92,14 @@ or
 .Fl E
 can be specified.
 .It Fl M
-Extract values associated with the name list from the specified core
-instead of the default
-.Pa /dev/kmem .
+Deprecated and ignored.
 .It Fl m
 Report the mount options for all NFS client mounts.
 This option overrides all others and
 .Nm
 will exit after completing the report.
 .It Fl N
-Extract the name list from the specified system instead of the default
-.Pa /boot/kernel/kernel .
+Deprecated and ignored.
 .It Fl s
 Only display server side statistics.
 .It Fl W
@@ -134,13 +129,6 @@ See
 .Xr xo_parse_args 3
 for details on command line arguments.
 .El
-.Sh FILES
-.Bl -tag -width ".Pa /boot/kernel/kernel" -compact
-.It Pa /boot/kernel/kernel
-default kernel namelist
-.It Pa /dev/kmem
-default memory file
-.El
 .Sh SEE ALSO
 .Xr fstat 1 ,
 .Xr netstat 1 ,