No longer are orbiting/trailing objects in charge of removing themselves.

	* They're clearly not quick enough at the job, since it causes a bunch of silly race conditions.
	* Instead, K_UpdateHnextList and K_CleanHnextList are in charge of removing them, which are called in the circumstances itemamount (and itemheld/eggmanheld) is changed.
	* Also, tweak a few places so that trailers AND orbiters can use the same system.
Also, some minor thingies.
	* Turn all the useless ```if (a) { A } else if (!a) { B }``` bullshit into ```if (a) { A } else { B }``` bullshit.
	* Fix up some minor inaccuracies in the playerarrow stuff that doesn't result in creating more sprites.