Deletes monkey tail DNA block, minor sprite accessory cleanup, monkeys (and lizardpeople) will no longer random spawn without tails (#85112)

## About The Pull Request

- Deletes monkey tail DNA block
- This is not something DNA blocks should be used for. If your only
options are "exists" or "doesn't exist", it doesn't need a DNA block,
you should just remove the tail!

- Minor sprite accessory cleanup
- Replaces a lot of blank SAs with `add_blank` usage. Tested in game and
it works.
- No reason to copy-paste blanks when we have a designated function for
it.

- Randomizing features can no longer select locked features
   - Bugfix, though it doesn't affect us at the moment.

- Monkeys (and lizard people) will no longer random into being tailless
- Felinids can still random into tailless (though that function is
broken ATM)

## Why It's Good For The Game

For the tailless change: 

It's a bit weird for these species to spawn without tails. They're kinda
a huge part of their identity.
I left in the tailless Sprite Accessory, however, so you can still
select them in the prefs menu.

## Changelog

🆑 Melbert
qol: All randomly spawned monkeys (and lizardpeople) will spawn with
tails. You can still select to be tailless.
code: Cleaned up some code relating to species features (like tails,
markings, etc). Report any oddities
/🆑

code/modules/surgery/organs/external/tails.dm

@@ -175,7 +175,7 @@
 
 	bodypart_overlay = /datum/bodypart_overlay/mutant/tail/monkey
 
-	dna_block = DNA_MONKEY_TAIL_BLOCK
+	dna_block = null
 
 ///Monkey tail bodypart overlay
 /datum/bodypart_overlay/mutant/tail/monkey