Description:
------------
when you or php calls header(XY)

is impossible to delete this header

(yes can overwrite it... but cant delete it)

PS: headers are not sent to client

Reproduce code:
---------------
try this
php.ini set output_buffering = ob_gzhandler

index.php
<?php
ob_end_clean();
ob_start(null, 4096, true);
?>

client writes encoding mismatch... because in index.php is impossible to delete header Vary and Content-Encoding




Expected result:
----------------
if exists function header_list

why doesnt exists function header_delete

Actual result:
--------------
see above