These functions would have caused a `-Woverloaded-virtual` warning with
GCC 13, as they shadow `File::{attach,detach}(OpenFileDescription&)`.
Both of these functions had a single call site. This commit inlines
`attach` into its only caller, `FIFO::open_direction`.
Instead of explicitly checking `is_fifo()` in `~OpenFileDescription`
before running the `detach(Direction)` overload, let's just override the
regular `detach(OpenFileDescription&)` for `FIFO` to perform this action
instead.
2123fdd678