patch nuke-the-dbuf-hash

@@ -176,15 +176,10 @@
          * May change from NULL to non-NULL under the protection of db_mtx
          * (see dbuf_check_blkptr())
          */
         struct dmu_buf_impl *db_parent;
 
-        /*
-         * link for hash table of all dmu_buf_impl_t's
-         */
-        struct dmu_buf_impl *db_hash_next;
-
         /* our block number */
         uint64_t db_blkid;
 
         /*
          * Pointer to the blkptr_t which points to us. May be NULL if we