The function introduced in https://github.com/jwiegley/use-package/issues/673 wasn't declared at compile time, and
it made byte compiler unhappy. Moreover, it was forgotten to remove
redundant compile time variables. Thanks @tarsius for pointing that
out.
This change
* Removes redundant variable declarations
* Adds `system-packages-get-command` function declaration.
Copyright-paperwork-exempt: yes
ensure-system-package doesn't honor system-packages
customizations (https://github.com/jwiegley/use-package/issues/661), because system-packages didn't provide an API
to retrieve shell command to be executed.
This change makes use of the new system-packages'
`system-package-get-command` function and therefore fixes the issue.
GitHub-reference: fix https://github.com/jwiegley/use-package/issues/661
Copyright-paperwork-exempt: yes
