md(4): Stop symlinking vn.4 to md.4

We've done the same in the past to the vnconfig.8->mdconfig.8 link in:
    eb5f456981 Remove ancient vnconfig symlink

Reviewed by:	bcr, markj, ziaee
Approved by:	markj (mentor)
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D27122

ObsoleteFiles.inc

@@ -51,6 +51,9 @@
 #   xargs -n1 | sort | uniq -d;
 # done
 
+# 20250716: Remove an old manual page, vn(4) was removed in FreeBSD 5.0
+OLD_FILES+=usr/share/man/man4/vn.4.gz
+
 # 20250710: share: Delete bitrotted make_*_driver.sh scripts
 OLD_FILES+=usr/share/examples/drivers/README
 OLD_FILES+=usr/share/examples/drivers/make_device_driver.sh

share/man/man4/Makefile

@@ -746,7 +746,6 @@ MLINKS+=lge.4 if_lge.4
 MLINKS+=lo.4 loop.4
 MLINKS+=lp.4 plip.4
 MLINKS+=malo.4 if_malo.4
-MLINKS+=md.4 vn.4
 MLINKS+=mem.4 kmem.4
 MLINKS+=mfi.4 mfi_linux.4 \
 	mfi.4 mfip.4

share/man/man4/md.4

@@ -5,7 +5,7 @@
 .\" this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
 .\" ----------------------------------------------------------------------------
 .\"
-.Dd January 8, 2020
+.Dd July 16, 2025
 .Dt MD 4
 .Os
 .Sh NAME
@@ -158,7 +158,7 @@ installation process.
 The
 .Nm
 driver did a hostile takeover of the
-.Xr vn 4
+.Sy vn
 driver in
 .Fx 5.0 .
 .Sh AUTHORS

sys/dev/md/md.c

@@ -11,9 +11,9 @@
  */
 
 /*-
- * The following functions are based on the vn(4) driver: mdstart_swap(),
- * mdstart_vnode(), mdcreate_swap(), mdcreate_vnode() and mddestroy(),
- * and as such under the following copyright:
+ * The following functions are based on the historical vn(4) driver:
+ * mdstart_swap(), mdstart_vnode(), mdcreate_swap(), mdcreate_vnode()
+ * and mddestroy(), and as such under the following copyright:
  *
  * Copyright (c) 1988 University of Utah.
  * Copyright (c) 1990, 1993