The ioutil functions are deprecated since Go 1.17 and only wrap another
library function. Thus directly call the underlying function.
This commit only mechanically replaces the function calls.
This functionality has gone unused since
4b3dc415ef41593fdd5e3cc0db3b78b3bbef5411 changed hashing.Reader's only
client to use ioutil.ReadAll on a bufio.Reader wrapping the hashing
Reader.
Reverts bcb852a8d0a674c5131668baae0826578f2e588a.