Properly removes Diablerist quirk

[boy2mantwicethefam]

Turns out that the mysterious "Test Quirk" was actually the remnants of the "Black Secret" quirk that was removed shortly after the codebase was forked from VtM13, which turns your character into a diablerist (does not affect the preferences, so removing the quirk removes the diablerist status unless you diablerized someone). This PR properly disables it.

I am not deleting the comment to clean up the codebase, it's a little piece of history.

[Metekillot]

Suggested change

	/datum/quirk/diablerist/on_spawn()
	if(iswerewolf(quirk_holder) || isgarou(quirk_holder))
	return
	var/mob/living/carbon/human/H = quirk_holder
	H.diablerist = TRUE
	*/

We have git for the history of the repo. That's like, all that git is for.

[boy2mantwicethefam]

Doesn't show up unless someone specifically tries to dig it up, which is pretty rare (only really involves using git blame).
I prefer leaving it commented out, the worst it does is having "diablerist" show up a few more times when searching for words in a codebase but it's basically microscopic since the codebase isn't massively cluttered with random comments that would actually be problematic when trying to code.