Revert "fallout from unified stdio"

This reverts commit a96e284a7e8e69c54b9b880e8591b5ec258802c2.
Revert "std: io: introduce a unified `stdio` object"

This reverts commit a0fd4ae45075ef1fc631b07427602c4e6d9b3888.
std: io: flush stdout on stdin read from tty