Rollup merge of #138457 - bjorn3:redox_scheme_paths, r=Noratrieb

Remove usage of legacy scheme paths on RedoxOS

The `name:/path` path syntax is getting phased out[^1] in favor of `/scheme/name/path`. Also using `null:` is no longer necessary as `/dev/null` is available on Redox OS too.

[^1]: https://gitlab.redox-os.org/redox-os/rfcs/-/blob/master/text/0006-scheme-path.md

cc `@jackpot51`

Author: jhpratt