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.

docs/book.toml

@@ -1,6 +1,6 @@
 [book]
 title = "Kaptan documentation"
-description = "Architecture, board bring-up, simulation, and contributor guidance for Kaptan."
+description = "Architecture, board bring-up, and contributor guidance for Kaptan."
 authors = ["Kaptan contributors"]
 language = "en"
 src = "src"