io/ioutil Deprecation Warnings

[nirosys]

Below are a few lints that are coming up with staticcheck. Our GHAs are currently configured to only show new lints, so these may be getting hidden due to that. The deprecation of io/ioutil is something that should be addressed since the package will at some point be removed.

• hash_reader_test.go:19:2: "io/ioutil" has been deprecated since Go 1.19: As of Go 1.16, the same functionality is now provided by package [io] or package [os], and those implementations should be preferred in new code. See the specific function documentation for details. (SA1019)
• hash_writer_test.go:20:2: "io/ioutil" has been deprecated since Go 1.19: As of Go 1.16, the same functionality is now provided by package [io] or package [os], and those implementations should be preferred in new code. See the specific function documentation for details. (SA1019)
• ion_hash_test.go:20:2: "io/ioutil" has been deprecated since Go 1.19: As of Go 1.16, the same functionality is now provided by package [io] or package [os], and those implementations should be preferred in new code. See the specific function documentation for details. (SA1019)

The functionality removed was scattered between io and os. Some more info here, with links to the proposals that this comes from.