f2fs: do not skip dentry block writes

Previously, we skip dentry block writes when wbc is SYNC_NONE with no memory
pressure and the number of dirty pages is pretty small.

But, we didn't skip for normal data writes, which gives us not much big impact
on overall performance.
Moreover, by skipping some data writes, kworker falls into infinite loop to try
to write blocks, when many dir inodes have only one dentry block.

So, this patch removes skipping data writes.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.h

@@ -118,7 +118,6 @@ static inline void raw_nat_from_node_info(struct f2fs_nat_entry *raw_ne,
 enum mem_type {
 	FREE_NIDS,	/* indicates the free nid list */
 	NAT_ENTRIES,	/* indicates the cached nat entry */
-	DIRTY_DENTS,	/* indicates dirty dentry pages */
 	INO_ENTRIES,	/* indicates inode entries */
 	EXTENT_CACHE,	/* indicates extent cache */
 	BASE_CHECK,	/* check kernel status */