This is a mix of more automated and manual migration. It should remove all applicable extension_loaded() checks outside of skipif.inc files.
The mb_http_input_pass.phpt was intended to use the same encoding as mb_http_input.phpt, not UTF-8.
"pass" is not a real encoding, it just means "don't perform any conversion". Using it as an internal encoding or passing it to any of the mbstring() function will not work (and on master commonly assert).
Nikita Popov