sys: Correct osreldate descriptions

The kern.osreldate sysctl reports the kernel version, not a release
date.  Also correct a comment about /usr/include/osreldate.h.

Reviewed by:	kp, olce
Event:		Kitchener-Waterloo Hackathon 202506
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D50938

sys/kern/kern_mib.c

@@ -574,12 +574,11 @@ sysctl_osreldate(SYSCTL_HANDLER_ARGS)
 }
 
 /*
- * NOTICE: The *userland* release date is available in
- * /usr/include/osreldate.h
+ * NOTICE: The *userland* version is available in /usr/include/osreldate.h
  */
 SYSCTL_PROC(_kern, KERN_OSRELDATE, osreldate,
     CTLTYPE_INT | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
-    NULL, 0, sysctl_osreldate, "I", "Kernel release date");
+    NULL, 0, sysctl_osreldate, "I", "Kernel version");
 
 /*
  * The build-id is copied from the ELF section .note.gnu.build-id.  The linker