Runtime errors thrown in aliases.php under PHP8+

A runtime error is thrown for most of class alias defined in `src/aliases.php` of this kind:

> Cannot declare class google\appengine\api\modules\InvalidModuleStateException, because the name is already in use

Given that [PHP namespaces are case-insensitive](https://www.php.net/manual/en/language.namespaces.rationale.php), most of the alias defined there are not necessary, as the old php55 sdk names are case-insensitive equal to the php7+ SDK.