ext4: remove unused macro MPAGE_DA_EXTENT_TAIL

Remove unused macro MPAGE_DA_EXTENT_TAIL which
is no more used after below commit
4e7ea81d ("ext4: restructure writeback path")
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200101095137.25656-1-riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -48,8 +48,6 @@
 
 #include <trace/events/ext4.h>
 
-#define MPAGE_DA_EXTENT_TAIL 0x01
-
 static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
 			      struct ext4_inode_info *ei)
 {