JsonStrategy should not set content-transfer-encoding response header

[weierophinney]

As of zendframework/zendframework#3483, JsonStrategy adds the Content-Transfer-Encoding header when using UTF-16 or UTF-32. I believe doing so is incorrect, as Content-Transfer-Encoding is a MIME header, not an HTTP header.

https://tools.ietf.org/html/rfc7231#appendix-A.5:

HTTP does not use the Content-Transfer-Encoding field of MIME.
Proxies and gateways from MIME-compliant protocols to HTTP need to
remove any Content-Transfer-Encoding prior to delivering the response
message to an HTTP client.

Apparently the confusion originated with a comment on that pull request, which is probably due to a misunderstanding of the poorly described "encoding considerations" of https://tools.ietf.org/html/rfc4627#section-6. The confusing reference to content-transfer-encoding was removed in the RFC that replaced it.

See issue #61, which was also introduced by zendframework/zendframework#3483.

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Originally posted by @ademarre at zendframework/zend-view#62