Available inall subroutines.
Deletes a header by name.
This is equivalent to the
unset statement except that the header name
is given as a string, and may be passed dynamically.
Header names are case insensitive.
The where argument is one of the literal identifiers
is equivalent to:
header.unset for a header which does not exist, or passing the empty string,
a not-set value, or a string that would be invalid as a header name,
also has no effect.
header.set for valid characters in header names.