Convert remaining '= Buffer(stuff)' to 'Buffer.from(stuff,...)'

[vladikoff]

Here are some:

[vladikoff]

cc @deeptibaghel

[deeptibaghel]

I will do it @vladikoff :)

[vladikoff]

@deeptibaghel thank you! This should be easier than the other one, there are more occurrences of this in the auth server mozilla/fxa-auth-server#2333