xfs: extend removed sysctls table

Commit 21d59d00 ("xfs: remove deprecated sysctl knobs") moves
recently-removed sysctls to the removed sysctls table but fails to
extend the table, hence triggering Sphinx warning:

Documentation/admin-guide/xfs.rst:365: ERROR: Malformed table.
Text in column margin in table line 8.

=============================   =======
  Name                          Removed
=============================   =======
  fs.xfs.xfsbufd_centisec       v4.0
  fs.xfs.age_buffer_centisecs   v4.0
  fs.xfs.irix_symlink_mode      v6.18
  fs.xfs.irix_sgid_inherit      v6.18
  fs.xfs.speculative_cow_prealloc_lifetime      v6.18
=============================   ======= [docutils]

Extend "Name" column of the table to fit the now-longest sysctl, which
is fs.xfs.speculative_cow_prealloc_lifetime.

Fixes: 21d59d00 ("xfs: remove deprecated sysctl knobs")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/linux-next/20250908180406.32124fb7@canb.auug.org.au/


Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>