Delete old devcontainer package from GitHub Container Registry

## Summary

The old devcontainer package should be deleted from the GitHub Container Registry as it has been superseded by the new one.

## Details

The old package `ghcr.io/bytecodealliance/sample-wasi-http-rust-devcontainer` used a hyphenated name. As of #76, the devcontainer now publishes to `ghcr.io/bytecodealliance/sample-wasi-http-rust/devcontainer` using the nested path pattern consistent with the main wasm component.

## Action Required

- [ ] Delete `ghcr.io/bytecodealliance/sample-wasi-http-rust-devcontainer` from the container registry
- [ ] Verify users can pull the new image at `ghcr.io/bytecodealliance/sample-wasi-http-rust/devcontainer`

cc @yoshuawuyts

## References

- #50 - Original issue for fixing devcontainer publish
- #76 - PR that updated the image path