unblacklists botany fruits and vegetables from unit tests. (#89683)

## About The Pull Request
subtypes of `/obj/item/food/grown` have no reason to not be spawned by
the `create_and_destroy` unit test, which prevents us from knowing if a
type fruit or veggie doesn't have a set seed in the tests. The only path
that needs to be blacklisted is the common `/obj/item/food/grown` path
itself, since its seed variable needs to remain null so that we can be
warned about any subtype that hasn't overriden that value.
This PR also removes the `/obj/item/food/grown/shell` path which serves
no purpose anymore.

## Why It's Good For The Game
Backend improvements. Atomizing changes from my refactor.

## Changelog
N/A

code/modules/unit_tests/food_edibility_check.dm

@@ -7,7 +7,7 @@
 		/obj/item/food/grown/mushroom,
 		/obj/item/food/clothing,
 		/obj/item/food/meat/slab/human/mutant,
-		/obj/item/food/grown/shell)
+	)
 
 	var/list/food_paths = subtypesof(/obj/item/food) - not_food
 

code/modules/unit_tests/unit_test.dm

@@ -271,6 +271,9 @@ GLOBAL_VAR_INIT(focused_tests, focused_tests())
 		/obj/item/organ/wings,
 		//Not meant to spawn without the machine wand
 		/obj/effect/bug_moving,
+		//The abstract grown item expects a seed, but doesn't have one
+
+		/obj/item/food/grown,
 	)
 
 	// Everything that follows is a typesof() check.
@@ -286,8 +289,6 @@ GLOBAL_VAR_INIT(focused_tests, focused_tests())
 	returnable_list += typesof(/obj/item/modular_computer/processor)
 	//Very finiky, blacklisting to make things easier
 	returnable_list += typesof(/obj/item/poster/wanted)
-	//This expects a seed, we can't pass it
-	returnable_list += typesof(/obj/item/food/grown)
 	//Needs clients / mobs to observe it to exist. Also includes hallucinations.
 	returnable_list += typesof(/obj/effect/client_image_holder)
 	//Same to above. Needs a client / mob / hallucination to observe it to exist.