Revert "Use ruamel.yaml as default yaml parser."
Revert "Use ruamel.yaml as default yaml parser."

This reverts commit 4e1022b7ffef6a8afc5a6832ad983ca38d0819cd.

davidwaroquiers/monty,materialsvirtuallab/monty,davidwaroquiers/monty,gmatteo/monty,gmatteo/monty,materialsvirtuallab/monty