Revert shared_ptr<io_data_t> changes until kinks are ironed out
https://github.com/fish-shell/fish-shell/pull/487

Revert "Merge branch 'oo-io' of git://github.com/xiaq/fish-shell into xiaq-oo-io"

This reverts commit f3c8f535a48d5fdd518bd60879ade948bc8be7e6, reversing
changes made to b02f6cf3bc4343cf3e068dee3cb46de7139a5a27.

Also reverts ac023f7588e562a03fdea7fd2feda487f18827c7 and a79d3c680c9548566309121630dadc94e48934c4