Remove the leftover element factories of the malspp testbed

LargeEnumerationFactory and MediumEnumerationFactory are left over from an
earlier design, where an element was registered through a factory of its
own. They extend MALElementsRegistry and declare a createElement() that
takes no argument, so they override nothing on it, and nothing refers to
either of them.

They were also the only classes extending MALElementsRegistry, so removing
them leaves it free to change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: CesarCoelho