Remove optional package loading to simplify pool builder

[naderman]

Instead we just directly check if any currently loaded package requires the package to be loaded optionally.

[Toflar]

I did it the other way around to loop over $this->packages only once but I guess at this point it's not a big deal.

[naderman]

Yeah I think since this is now only for deps of the allow-listed packages and $this->packages should mostly contain locked/fixed packages at that point it really shouldn't make a measurable performance difference.