refactor(firmware): remove the retired simulation workflow

Remove the retired simulator workspace member, dependencies, workflow
and documentation. Keep the shared flight and hardware crates.

Validation: retirement prefix host check, command-dispatch tests and
book build.

firmware/Cargo.toml

@@ -26,7 +26,6 @@ members = [
   "libs/kaptan-time",
   "libs/kaptan-tx",
   "platforms/stm32f7",
-  "tools/sitl",
   "tools/configurator",
 ]
 resolver = "2"