Fix lots of Greentea test warnings

[multiplemonomials]

Summary of changes

Ever since I've started on Mbed CE, there have been ludicrous amounts of warnings every time the greentea tests are compiled. The vast majority of these are due to tests using deprecated API, especially legacy RTOS functions that don't use chrono types. This PR fixes at least 90% of these warnings, so the greentea build is now a much more warning-free experience. There are still a few here and there but it's a lot better now at least.

Someday I want to fix all of the warnings and then make the CI builds use -Werror but... not today.

Impact of changes

Way less warnings in Greentea test builds

Migration actions required

Documentation

None

---

Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---