inode->in_lru_list is not really used

[mykaul]

ykaul@ykaul:~/github/glusterfs$ grep -Frisn in_lru_list
libglusterfs/src/glusterfs/inode.h:118:    bool in_lru_list;         /* Set if inode is in table lru list */
libglusterfs/src/inode.c:414:    GF_ASSERT(!inode->in_lru_list);
libglusterfs/src/inode.c:417:    inode->in_lru_list = _gf_true;
libglusterfs/src/inode.c:557:            GF_ASSERT(inode->in_lru_list);
libglusterfs/src/inode.c:559:            inode->in_lru_list = _gf_false;
libglusterfs/src/inode.c:693:            GF_ASSERT(!inode->in_lru_list);
libglusterfs/src/inode.c:694:            inode->in_lru_list = _gf_true;
libglusterfs/src/inode.c:1585:            GF_ASSERT(entry->in_lru_list);
libglusterfs/src/inode.c:1603:            entry->in_lru_list = _gf_false;
libglusterfs/src/inode.c:1654:    root->in_lru_list = _gf_true;
libglusterfs/src/inode.c:1867:            GF_ASSERT(trav->in_lru_list);
libglusterfs/src/inode.c:1870:            trav->in_lru_list = _gf_false;

So it's not really used anywhere but in assertions. We can #ifdef this to DEBUG only perhaps.

CC @mohit84