core: do not print color console message about gc-ed jobs

This is just a cosmetic issue.

Garbage collection of jobs (especially the ones that we create automatically)
is something of an internal implementation detail and should not be made
visible to the users. But it's probably still useful to log this in the
journal, so the code is rearranged to skip one of the messages if we log to the
console and the journal separately, and to keep the message if we log
everything to the console.

Fixes #6254.