Remove RalfJung from gpu-target.toml

[ZuseZ4]

Per request in rust-lang/rust#149793 (comment)

[github-actions]

Dry-run check results

[WARN  rust_team::sync] sync-team is running in dry mode, no changes will be applied.
[INFO  rust_team::sync] synchronizing crates-io
[INFO  rust_team::sync] synchronizing github
[INFO  rust_team::sync] 💻 Team Diffs:
    📝 Editing team 'rust-embedded/risc-v':
      Adding member 'rmsyn' with member role

[RalfJung]

Thanks! I saw this only now.
This is superseded by #2419.