remove content_type from response

[olirice]

Remove the content_type field from net._http_response since it is a header and there is already a field for that
https://github.com/supabase/pg_net/blob/master/sql/pg_net--0.1.sql#L22

[steve-chavez]

+1 to this one. Otherwise we have to guard for cases where there's no content-type in the worker.

Already done here, but still less code is better.