stitch doesn't use "trivial"

[EliahKagan]

The stitch script is not using the trivial variable:

extents/stitch

Line 81 in 5912d5d

# $trivial matches fiemap's last output line for an empty file (no captures).

The shellcheck run, correctly performed since #5, reveals that it is unused:

https://github.com/EliahKagan/extents/actions/runs/4151965951/jobs/7182603038#step:3:25

That warning appears to be correct.

I'm not sure how I missed this, because although shellcheck was not being correctly run via CI prior to #5, I did run it myself when developing extents, as well as test the case where the file being examined and recreated is empty. But indeed, I do not seem to ever actually use the trivial variable. This needs to be looked into.