generic/340: Remove second fallocate test

generic/340: Remove second fallocate test

Currently holetest program uses both posix_fallocate(3) and fallocate(3)
to setup the file. However this unnecessarily prolongs the test run and
doesn't really bring any additional code coverage. So remove the
fallocate(3) pass as using posix_fallocate(3) allows us to make the test
easily runnable even for filesystems not supporting that (such as ext2).

Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>