xfs: Remove deprecated xfs_bufd sysctl parameters

Commit 64af7a6e ("xfs: remove deprecated sysctls") removed the
deprecated xfsbufd-related sysctl interface, but forgot to delete the
corresponding parameters: "xfs_buf_timer" and "xfs_buf_age".

This patch removes those parameters and makes no other changes.

Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>