Remove mentions of MAP_COPY, it's not available and trying to use it

will result in compile failure.

lib/libc/sys/mmap.2

@@ -1,4 +1,4 @@
-.\"	$NetBSD: mmap.2,v 1.39 2007/07/18 23:34:23 wiz Exp $
+.\"	$NetBSD: mmap.2,v 1.40 2009/02/27 16:23:54 pooka Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -29,7 +29,7 @@
 .\"
 .\"	@(#)mmap.2	8.4 (Berkeley) 5/11/95
 .\"
-.Dd October 6, 2003
+.Dd February 27, 2009
 .Dt MMAP 2
 .Os
 .Sh NAME
@@ -107,10 +107,9 @@ parameter specifies the type of the mapped object, mapping options and
 whether modifications made to the mapped copy of the page are private
 to the process or are to be shared with other references.
 Note that either
-.Dv MAP_SHARED ,
-.Dv MAP_PRIVATE
+.Dv MAP_SHARED
 or
-.Dv MAP_COPY
+.Dv MAP_PRIVATE
 must be specified.
 Sharing, mapping type and options are specified in the
 .Fa flags
@@ -177,8 +176,6 @@ other processes using
 will be seen.
 .It Dv MAP_SHARED
 Modifications are shared.
-.It Dv MAP_COPY
-Modifications are private, including other processes.
 .El
 .Pp
 The
@@ -286,12 +283,3 @@ would exceed the offset maximum established in its open file description.
 .Xr munmap 2 ,
 .Xr getpagesize 3 ,
 .Xr sysconf 3
-.Sh BUGS
-The
-.Dv MAP_COPY
-flag is not implemented.
-The current
-.Dv MAP_COPY
-semantics are the same as those of the
-.Dv MAP_PRIVATE
-flag.