LU-12542 handle: discard h_lock.

LU-12542 handle: discard h_lock.

The h_lock spinlock is now only taken while bucket->lock
is held.  As a handle is associated with precisely one bucket,
this means that h_lock can never be contended, so it isn't needed.

So discard h_lock.

Also discard an increasingly irrelevant comment in the declaration
of struct portals_handle.

Change-Id: Ib5231fb43d1bf5031d5c2426c4e1d1865544bcf5
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-on: https://review.whamcloud.com/35863
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>