Check the need for active.set(false); in Entity::clean

[AlmasB]

It appears active is always false at that point, in which case the call is redundant and can be removed:

FXGL/fxgl-entity/src/main/java/com/almasb/fxgl/entity/Entity.java

Lines 188 to 191 in bbf2bb9

	// TODO: we probably don't need to set active false again, since we do that in markForRemoval?
	active.set(false);
	}

I have looked at call sites for clean() in GameWorld and they are always preceded by marForRemoval()

FXGL/fxgl-entity/src/main/java/com/almasb/fxgl/entity/Entity.java

Lines 259 to 262 in bbf2bb9

	void markForRemoval() {
	onNotActive.run();
	active.set(false);
	}

So, active is false. This code is in a robust-critical section, so I'd like a second review.

@adambocco could you double check the clean() call sites and see if it is somehow possible for active to be true before it reaches clean.