net/rds: remove unused struct 'rds_ib_dereg_odp_mr'

'rds_ib_dereg_odp_mr' has been unused since the original
commit 2eafa1746f17 ("net/rds: Handle ODP mr
registration/unregistration").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Reviewed-by: Allison Henderson <[e-mail]>
Reviewed-by: Zhu Yanjun <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/rds/ib_rdma.c

···
 #include "rds.h"
 
 struct workqueue_struct *rds_ib_mr_wq;
-struct rds_ib_dereg_odp_mr {
-	struct work_struct work;
-	struct ib_mr *mr;
-};
 
 static void rds_ib_odp_mr_worker(struct work_struct *work);