Remove implicit dependency on `time 0.1`

chrono, by default, depends on an old version of time, which has a RUSTSEC: https://github.com/emilk/egui/security/dependabot/7

egui doesn't use chrono, but egui_extras does as does egui_demo_lib. It would be nice to replace it with pure time 0.3 use, or use achrono without the oldtime feature it has.

It's worth noting that next release of chrono seem to have removed the dependency on time completely, so maybe this will sort itself out in time