Remove pin from strictyaml

[prusse-martin]

Remove the pin from strictyaml (added in 0.10.1) and remove explicit ruamel.yaml dependency.
In strictyaml==1.4.4 ruamel is bundled and explicit uses of ramuel cause conflicts with the bundled version.
We should remove the strictyaml pin (and ruamel dep) to update the code to more recent versions.

(It was not updated now to avoid problems with the version of alfasim in release process)