LU-9679 obdclass: don't manage module refs in open/close.

LU-9679 obdclass: don't manage module refs in open/close.

Core Linux code for managing char-devs ensures that the relevant
module is held active while a char-dev is open - see cdev_get()
and cdev_put().
So there is no need for lustre/obd_class to manage the module
ref count as well.

As this is all that obd_class_open and obd_class_close do, those
functions can be removed.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I84b0dc81c830cefc2383f184d12beeb2cfa22404
Reviewed-on: https://review.whamcloud.com/37021
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>