Remove the usage Serialization yaml mapper

[shawkins]

The yaml mapper is mostly not needed and can be avoided entirely with logic similar to what is done for parsing. This will also remove the need for the method to clear the mapper.

[andreaTP]

The yaml mapper is used under the scenes by the java generator as most of the provided CRDs are in yaml format.

What would be a viable substitution for it?

[shawkins]

@andreaTP the unmarshal methods and asYaml will handle deserialization and serialization. Do you have a scenario that requires direct access to the mapper?

[andreaTP]

In the java-generator we are only using the high level: Serialization.unmarshal, so I should be good 👍