Remove @JsonTypeName from jersey2 POJOs

A sibling PR to #14842 and #14852. This PR removes the @JsonTypeName annotation from the jersey2 templates. I want to make some other changes that affect the handling of the @JsonTypeName annotation, and investigating those issues led to the conclusion that @JsonTypeName is unnecessary, as the name of the type is specified in the super class' @JsonSubTypes annotation wherever necessary.

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