Documentation: update epoll sysctl text

max_user_instances was removed in this commit:

   commit 9df04e1f25effde823a600e755b51475d438f56b
   Author: Davide Libenzi <davidel@xmailserver.org>
   Date:   Thu Jan 29 14:25:26 2009 -0800

    epoll: drop max_user_instances and rely only on max_user_watches

but the documentation entry was not removed.

Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Lucian Adrian Grijincu <lucian.grijincu@gmail.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/sysctl/fs.txt

@@ -231,13 +231,6 @@ its creation).
 
 This directory contains configuration options for the epoll(7) interface.
 
-max_user_instances
-------------------
-
-This is the maximum number of epoll file descriptors that a single user can
-have open at a given time. The default value is 128, and should be enough
-for normal users.
-
 max_user_watches
 ----------------