LU-11783 build: remove lustre_user.h deprecation warning

LU-11783 build: remove lustre_user.h deprecation warning

The "lustre/lustre_user.h" header has been in use for many years.
The patch https://review.whamcloud.com/25246 "LU-6401 uapi: migrate
remaining uapi headers to uapi directory" moved the header to
"linux/lustre/lustre_user.h" and left a stub "lustre/lustre_user.h"
behind that generates a compiler warning that this header is
deprecated.

However, no window was given between the introduction of the new
header and the deprecation of the old header, which makes it harder
for applications to smoothly transition to the new header location.
Also, installing Lustre headers into the "linux/" directory before
Lustre is actually part of the kernel may potentially cause problems.

Disable the deprecation warning in the old header for several
releases, until the new header location has been available for a good
time and it is safe for applications to assume that it is available.

Test-Parameters: trivial
Fixes: 6712478e79588e73e28c7ccac3afc7ac2368a4f3
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: If5a62587e2d3627178a0f7a09c3a4c10801cab07
Reviewed-on: https://review.whamcloud.com/33872
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>