Revert r326125.

It turns out kgmon(8) still works, and provides some functionality that's
not provided by pmcstat(8).

Reported by:	bde@
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL

usr.sbin/kgmon/kgmon.8

@@ -28,7 +28,7 @@
 .\"     @(#)kgmon.8	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd November 23, 2017
+.Dd June 6, 1993
 .Dt KGMON 8
 .Os
 .Sh NAME
@@ -40,13 +40,6 @@
 .Op Fl M Ar core
 .Op Fl N Ar system
 .Sh DESCRIPTION
-.Bf -symbolic
-This command is obsolete.
-Users are advised to use
-.Xr pmcstat 8
-instead.
-.Ef
-.Pp
 The
 .Nm
 utility is used when profiling the operating system.