guix: Clean up manifest

Summary:

guix: Unify fetch methods

guix: Drop unneeded modules

guix: Specify symbols in modules explicitly

This change improves the maintainability of the manifest:
(1) It allows to remove the module when the specified symbols are no longer used.
(2) It prevents accidental use of other symbols, such as bash instead of bash-minimal.

This is a backport of core#27811
Depends on D15344

Test Plan: contrib/guix/guix-build

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15345