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/scripts/report-test-coverage.sh

@@ -128,7 +128,6 @@ report_package kaptan-sensor /libs/kaptan-sensor/
 report_package kaptan-spi /libs/kaptan-spi/
 report_package kaptan-time /libs/kaptan-time/
 report_package kaptan-tx /libs/kaptan-tx/
-report_package kaptan-sitl /tools/sitl/
 
 echo "platform-stm32f7          target-only/N/A (run cargo check -p platform-stm32f7 --lib)"
 echo "kaptan-geprc-f722-v2      target-only/N/A (run its thumbv7em-none-eabihf check)"