Minor cleanup getRandomAlphanum

[jimhark]

Summary

cleanup getRandomAlphanum()

Fixes

Resolves #222

Details

• Removed unneeded "& 0xff" and related comment.
• Removed byteArray variable
• Renamed 'parsedInt' to randByte

Notes for Reviewers

While writing this description, I noticed 2 lines that should be removed:

const myAlphaNumTestValue = getRandomAlphanum();
let byteArray;

I'll submit a follow-up pull request to remove those lines.