ext4: use ext4_ext_next_allocated_block instead of mext_next_extent

This allows us to make mext_next_extent static and potentially get rid
of it.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2753,8 +2753,6 @@ extern void ext4_double_up_write_data_sem(struct inode *orig_inode,
 extern int ext4_move_extents(struct file *o_filp, struct file *d_filp,
 			     __u64 start_orig, __u64 start_donor,
 			     __u64 len, __u64 *moved_len);
-extern int mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
-			    struct ext4_extent **extent);
 
 /* page-io.c */
 extern int __init ext4_init_pageio(void);