LU-12542 lustre: remove INIT_LIST_HEAD_RCU support.

LU-12542 lustre: remove INIT_LIST_HEAD_RCU support.

Not all kernels provide INIT_LIST_HEAD_RCU() so it is provided for
older kernels.  But lustre no longer uses this macro and is unlikely
to - it is rarely used at all.

So remove the back-compat support.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I0556e9c75c575ee269f253a90600788747578593
Reviewed-on: https://review.whamcloud.com/37789
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>