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.lock

@@ -374,25 +374,6 @@ dependencies = [
  "kaptan-time",
 ]
 
-[[package]]
-name = "kaptan-sitl"
-version = "0.1.0"
-dependencies = [
- "kaptan-config",
- "kaptan-control",
- "kaptan-diagnostics-mavlink",
- "kaptan-err-reportable",
- "kaptan-flight-config",
- "kaptan-flight-runtime",
- "kaptan-log",
- "kaptan-math",
- "kaptan-mavlink",
- "kaptan-navigation",
- "kaptan-safety",
- "kaptan-time",
- "minicbor",
-]
-
 [[package]]
 name = "kaptan-spi"
 version = "0.1.0"