Bump external/elfio from 73a2410 to 47af3a4

Bumps [external/elfio](https://github.com/serge1/ELFIO) from `73a2410` to `47af3a4`.
- [Release notes](https://github.com/serge1/ELFIO/releases)
- [Commits](serge1/ELFIO@73a2410...47af3a4)

---
updated-dependencies:
- dependency-name: external/elfio
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>