LU-11085 lustre: remove interval-tree code

LU-11085 lustre: remove interval-tree code

The lustre interval tree is no longer used.  All users have been
changed to use the Linux interval tree implementation.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I7aaa79ebb5e672657dd96c79bd8f85cdf3ce5438
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49166
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>