Drop the `sys-info` dependency (#18324)
Part of https://github.com/astral-sh/uv/issues/14574 and
https://github.com/termux/termux-packages/issues/27547
Avoids the downstream patch at
https://github.com/termux/termux-packages/blob/master/packages/uv/0001-sys-info-replace-index-with-strchr.diff
`sys-info-rs` has not been updated in years
https://github.com/FillZpp/sys-info-rs — it includes C code and can't be
built on Termux https://github.com/FillZpp/sys-info-rs/issues/116
I considered switching to https://github.com/GuillaumeGomez/sysinfo but
our usage is trivial, so we implement our requirements in `uv-platform`
instead
