ext4: remove dead GET_BLOCKS_ZERO code

There's no call to ext4_map_blocks() in the current ext4 code with a
flags argument that combines EXT4_GET_BLOCKS_CONVERT and
EXT4_GET_BLOCKS_ZERO.  Remove the code that corresponds to this case
from ext4_ext_handle_unwritten_extents().

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20200430185320.23001-2-enwlinux@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -3829,14 +3829,6 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 	}
 	/* IO end_io complete, convert the filled extent to written */
 	if (flags & EXT4_GET_BLOCKS_CONVERT) {
-		if (flags & EXT4_GET_BLOCKS_ZERO) {
-			if (allocated > map->m_len)
-				allocated = map->m_len;
-			err = ext4_issue_zeroout(inode, map->m_lblk, newblock,
-						 allocated);
-			if (err < 0)
-				goto out2;
-		}
 		ret = ext4_convert_unwritten_extents_endio(handle, inode, map,
 							   ppath);
 		if (ret >= 0)