Avoid "Cannot redeclare class"

[NinoSkopac]

I am not very knowledgeable of this SDK, so this may be a stupid idea (tests will show), but if you opt in for require_once instead of require, you can't have the same class file re-required, which is a good thing.

[yguedidi]

👎 This is useless, as the autoloader is called for a class that is not loaded yet by PHP, once it's loaded, our autoload callback is no more called for that class :)

[SammyK]

Hey @NinoSkopac! Thanks for another PR! But again, I'm with @yguedidi on this one. The autoloader is based off of an official example from the PHP-FIG. In addition to require_once being slower than require, the autoloader won't be invoked again once a class is loaded so it's redundant to have require_once. :)

[NinoSkopac]

Yep, my bad <3