New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/24079#discussion_r466098367

Comment:
The `post-install` is too complicated. What about
```
REFIND_CONF="$(readlink -m "${ROOTDIR}/${REFIND_CONF:-boot/EFI/refind/refind.conf}" 2>/dev/null)"
[ -n "${REFIND_CONF}" ] || exit 0
```
Since we already rely on `cat`, which is in `coreutils` alongside `readlink`, I don't have a problem just assuming readlink exists. We also just assume `awk` and `sed` are available anyway.