LU-17606 ldiskfs: remove old compatibility code

LU-17606 ldiskfs: remove old compatibility code

The JOURNAL_START_HAS_3ARGS and EXT4_HT_MISC checks are always true
for kernels since 3.10, and no longer have any value to keep around.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I39333026b1f24c3d60fbc3f8c51be693353ebbe5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54274
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>