Don't autoload classes in AutoloadStructureTest

Don't autoload classes in AutoloadStructureTest

Autoloading classes is a 100% accurate way to ensure the autoloader
worked, but there are cases where if optional dependencies aren't
installed, then autoloading the class will fail. We can re-implement the
logic behind the PSR-4 autoloader, and ensure that classes will be
autoloadable by turning the filename into a class name, and making sure
that class name is the one we found in the file.

Bug: T195823
Change-Id: I5df378180e567c257386482383ef73812592f989