delete Other "Content-" MIME Header Fields exception
Motivation:
RFC7578 4.8. Other "Content-" Header Fields
The multipart/form-data media type does not support any MIME header
fields in parts other than Content-Type, Content-Disposition, and (in
limited circumstances) Content-Transfer-Encoding. Other header
fields MUST NOT be included and MUST be ignored.
Modification:
Ignore other Content types.
Result:
Other "Content-" Header Fields should be ignored no exception
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