sysctl: Remove (very) old file changelog

These comments are older than 2003 and therefore do not bare any
relevance on the current state of the sysctl.c file. Remove them as they
confuse more than clarify.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>