message-remove-header
message-remove-header is a compiled Lisp function in `message.el
'.
(message-remove-header HEADER &optional IS-REGEXP FIRST REVERSE)
Remove HEADER in the narrowed buffer.
If IS-REGEXP, HEADER is a regular expression.
If FIRST, only remove the first instance of the header.
If REVERSE, remove headers that doesn't match HEADER.
Return the number of headers removed.