ext4: delete path dealloc code in ext4_ext_handle_uninitialized_extents

Code deallocating the extent path referenced by an argument to
ext4_ext_handle_uninitialized_extents was made redundant with identical
code in its one caller, ext4_ext_map_blocks, by commit 37794732

.
Allocating and deallocating the path in the same function also makes
the code clearer.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>