LU-17606 ldiskfs: remove old el7.[678] patches/series

LU-17606 ldiskfs: remove old el7.[678] patches/series

Remove the old ldiskfs el7.[678] patch series files, and the resulting
patch files that are no longer referenced by any patch series file:

    ./contrib/scripts/clearpatches.sh -d

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I6727d88af1261c9b4090984ad8cab51a5dce7057
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54271
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>