NFS: remove unused wpages field from struct nfs_server

The wpages field is not serving any purpose since commit c63c7b05
("NFS: Fix a race when doing NFS write coalescing") which was merged in
v2.6.22-rc1. Remove it completely.

Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Link: https://lore.kernel.org/r/20250613094439.82338-2-ailiop@suse.com


Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>