vf_sub, vf_format: change license to LGPL

They were added to the "to deleted" list and never relicensed, because I
thought I'd delete them early. But it's possible that they'll stay in
mpv for a longer time, so relicense them. Still leaving them as
deprecated and scheduled for removal, so they can still be dropped once
there is a better way to deal with them, if they get annoying, or if a
better mechanism is found that makes them unnecessary.

All contributors agreed. There are some minor changes by people who did
not agree, but these are all not relevant or have been removed.