remove itertools

[blukai]

std can do what peeking_take_while does! nothing else is used from itertools.

[oberrich]

itertools will be needed in #3088, any particular reason we want to get rid of it?

[blukai]

I glanced over the changes in the referenced pr and have not spotted itertools there.

the whole reason for this change is me being curious why there's itertools in my dependency tree (cargo tree) (among other micro-dependencies); after quick inspection I discovered absolutely no evidence of its usefulness.

[oberrich]

Apologies for the confusion, I'm referring to the alias branch as per #3088 (comment) and see here for the relevant function.
It's a lot nicer to have this in one functional chain instead of having to do it the boring way.

Shouldn't be too much headache to merge my PR if you remove it on a second thought.