aufs doc: no more proc_mounts.patch

proc_mounts.patch in aufs5-standalone.git is gone since aufs5.8.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Documentation/filesystems/aufs/README

@@ -249,13 +249,6 @@ optional. When you meet some problems, they will help you.
   Supports a nested loopback mount in a branch-fs. This patch is
   unnecessary until aufs produces a message like "you may want to try
   another patch for loopback file".
-- proc_mounts.patch
-  When there are many mountpoints and many mount(2)/umount(2) are
-  running, then /proc/mounts may not show the all mountpoints.  This
-  patch makes /proc/mounts always show the full mountpoints list.
-  If you don't want to apply this patch and meet such problem, then you
-  need to increase the value of 'ProcMounts_Times' make-variable in
-  aufs-util.git as a second best solution.
 - vfs-ino.patch
   Modifies a system global kernel internal function get_next_ino() in
   order to stop assigning 0 for an inode-number. Not directly related to