Per https://github.com/calamares/calamares-extensions/issues/33,
https://github.com/calamares/calamares-extensions/issues/27,
https://github.com/calamares/calamares-extensions/issues/32 &
https://github.com/calamares/calamares-extensions/issues/34, -extensions is
getting merged into mainline, making this package redundant and no longer
supported. It should be removed.

Can you please explain in more detail why you think the
calamares-extensions package is now included in calamares?

The provided URLs do not support this claim.
New upstream is https://codeberg.org/Calamares/calamares-extensions

My read of the comment on Issue 33 above was that it would be integrated
into the main `calamares` package, however, this doesn't seem to have
taken place.

In saying that, I'd certainly agree with the "no longer supported" part
and won't disagree with removing it. At least the mobile component
hasn't been functional for well over a year, with little support
upstream for fixing it. I also don't believe anything outside of the
Mobian installer depends on it, and that isn't currently functional either.