Start removing chrono from dependencies

[connec]

This leaves only rcgen as a 'root cause' for including chrono:

chrono v0.4.19
├── rcgen v0.7.0
│   └── qjsonrpc v0.2.3
│       └── sn_api v0.38.0 (/Users/chris/repos/safe_network/sn_api)
├── rcgen v0.8.14
│   └── qp2p v0.24.0
│       └── safe_network v0.36.3 (/Users/chris/repos/safe_network/sn)
│           └── sn_api v0.38.0 (/Users/chris/repos/safe_network/sn_api)
├── yasna v0.3.2
│   └── rcgen v0.7.0 (*)
└── yasna v0.4.0
    └── rcgen v0.8.14 (*)

We should keep an eye on rustls/rcgen#65, and update qp2p/qjsonrpc when we can.

---

• 76daf91 chore: upgrade tracing-appender and tracing-subscriber

  These new versions have dropped their dependence on chrono, which has
  an active security advisory against it (RUSTSEC-2020-0159) which seems
  unlikely to be resolved.

  chrono is still being pulled in by qp2p (via rcgen), sn_api, and
  sn_launch_tool. This will be fixed in future commits.

• 3fe040f chore(sn): upgrade sn_launch_tool

  The new version uses the upgraded versions of tracing which no longer
  depend on chrono.

• f7e715a chore(sn_api): switch from chrono to time

  Due to the active security advisory against chrono (RUSTSEC-2020-0159)
  is makes sense to switch to a library that is not affected (though we
  are not using the affected APIs in chrono).