Heroku-24: Remove `libgcrypt20-dev`

[edmorley]

Since:

• All of the language bindings I could find for it were unpopular and not actively maintained. For example:
  • Ruby: https://github.com/chrisliaw/gcrypt (last commit 3 years ago, 0 stars, not published to rubygems.org)
  • Python: https://framagit.org/okhin/pygcrypt/ (last commit 6 years ago, 0 stars, close to zero PyPI downloads excl mirrors syncing)
• It's the dev package for the library extracted from GnuPG, and it's much more common to interact with the gpg CLI directly. eg: https://github.com/vsajip/python-gnupg (8 million downloads/month) which uses the CLI instead.

See: https://packages.ubuntu.com/noble/libgcrypt20-dev https://gnupg.org/software/libgcrypt/

Towards #266. GUS-W-15159536.