NFS: Remove unused variable "pages_ptr"

This variable is initialized to NULL and is never modified before being
passed to nfs_readdir_free_large_page().  But that's okay, because
nfs_readdir_free_large_page() only seems to exist as a way of calling
nfs_readdir_free_pagearray() without this parameter.  Let's simplify by
removing pages_ptr and nfs_readdir_free_pagearray().

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>