Correctly serialize review requests with only-fields

Review Request #10169 — Created Sept. 22, 2018 and submitted — Latest diff uploaded

Information

Review Board
release-4.0.x
ced1cf3...

Reviewers

If the dvcs_feature is disabled and a request is made to the review
request WebAPI resource with the only-fields/only_fields query/post
parameter set to a subset of fields that does not include the
created_with_history field, the server would raise an exception and
return a HTTP 500. This was because the field was already excluded from
the set of serialized fields.

We now are more defensive about removing this field so as not to raise a
KeyError if the field is not in the dictionary.

Ran unit tests.