ext4: remove single extent cache

Single extent cache could be removed because we have extent status tree
as a extent cache, and it would be better.

Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jan kara <jack@suse.cz>

fs/ext4/move_extent.c

@@ -764,9 +764,6 @@ out:
 		kfree(donor_path);
 	}
 
-	ext4_ext_invalidate_cache(orig_inode);
-	ext4_ext_invalidate_cache(donor_inode);
-
 	return replaced_count;
 }