LU-16518 lnet: fix unused-but-set-variable warnings

LU-16518 lnet: fix unused-but-set-variable warnings

Remove unused primary_nid variable in lnet_peer_merge_data()
to silence a Clang compiler warning.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ib66fd31c7acc08fa66578cd7ab571f278f98afe1
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58181
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Max Wang <wamax@amazon.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>