Rationale: It is only used in INSTALLATION-OS and doesn't make sense to be
used in another context, given that file systems now automatically pull their
dependencies since commit 45eac6cdf5c8d9d7b0c564b105c790d2d2007799 (services:
Add file system utilities to profile).
* gnu/system.scm (%base-packages-disk-utilities): Deprecate and rename to...
* gnu/system/install.scm (%installer-disk-utilities): ... this.
(installation-os) [packages]: Adjust accordingly.