This is the analog of 7b2c9223e7 for the
emoji cache; the only difference is that the existing code was working
correctly. It's still worth changing for improved robustness.
This commit re-arranges the arguments of `purge_unused_caches()`
function in order to remain consistent with other similar functions
in the library like `may_be_perform_caching()`.
Based on the `dry_run` flag, this function either purges the list
of directories passed to them or prints a listing of the directories
it would have purged/kept_back, had the `dry_run` flag been false.
Aditya Bansal
Tim Abbott
Harshit Bansal