removed deprecated Class::MOP::load_class() call

This fixes warnings about `Class::MOP::load_class` being deprecated. `Class::MOP::load_class` itself warns and then calls `Class::Load::load_class`: https://metacpan.org/source/ETHER/Moose-2.1212/lib/Class/MOP.pm#L73

As a nice side effect, this also removes the Class::MOP dependendency, so Moose is no longer an indirect dependency.