tests: remove pre-generated f_extent_htree image

tests: remove pre-generated f_extent_htree image

The f_extent_htree test depends on the "mke2fs -d" functionality
that did not exist in the maint branch when the patch was landed.
On master this functionality exists and should be used instead of
a pre-generated image.  That exercises the "mke2fs -d" functionality
as well as e2fsck better.

[ Fixed to add missing expect.pre.? files --tytso ]

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>