ubifs: remove broken lazytime support

When "ubifs: introduce UBIFS_ATIME_SUPPORT to ubifs" introduced atime
support to ubifs, it also added lazytime support.  As far as I can tell
the lazytime support is terminally broken, as it causes
mark_inode_dirty_sync to be called from __writeback_single_inode, which
will then trigger the locking assert in ubifs_dirty_inode.  Just remove
the broken lazytime support for now, it can be added back later,
especially as some infrastructure changes should make that easier soon.

Fixes: 8c1c5f26 ("ubifs: introduce UBIFS_ATIME_SUPPORT to ubifs")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Richard Weinberger <richard@nod.at>