libhb: remove hb_scan, as directed by TODO

[samhutchins]

Description of Change:

hb_scan is basically a wrapper around hb_scan_list, wrapping the path passed to it in a single-item list. There's a TODO left in there about removing it when all the UIs are updated.

The only 2 places it's still used (as far as I can tell) are by the CLI and by hb_json_job_scan. I've updated both places to use hb_scan_list instead.

I'm not actually sure if this is a good change or not, as it makes the call-sites a little messier. But it does make it easier to change the signature of hb_scan.

I think that removing the TODO comment is also a valid course of action, I don't think it's that bad having both hb_scan methods personally

Tested on:

• Windows 10+ (via MinGW)
• macOS 10.13+
• Fedora Linux

[galad87]

Maybe hb_scan_list can be renamed back to hb_scan.