Renames flatten_list proc to assoc_to_values (#93453)

## About The Pull Request

`/proc/flatten_list()` -> `/proc/assoc_to_values()`, also changes the
code doc to mirror the language of `assoc_to_keys()`'s code doc

## Why It's Good For The Game

Having a proc called `assoc_to_keys` that takes an associative list and
returns a list of the keys, and also having a proc that takes an
associative list and returns a list of the values, and the latter not
being called `assoc_to_values` is very funny

## Changelog
🆑
code: renamed flatten_list proc to assoc_to_values
/🆑

---------

Co-authored-by: Ghom <42542238+Ghommie@users.noreply.github.com>

code/game/objects/items/crab17.dm

@@ -22,7 +22,7 @@
 		var/turf/targetturf = get_safe_random_station_turf_equal_weight()
 		if (!targetturf)
 			return FALSE
-		var/list/accounts_to_rob = flatten_list(SSeconomy.bank_accounts_by_id)
+		var/list/accounts_to_rob = assoc_to_values(SSeconomy.bank_accounts_by_id)
 		var/mob/living/L
 		if(isliving(user))
 			L = user
@@ -201,7 +201,7 @@
  * Grabs the accounts to be robbed and puts them in accounts_to_rob, tells the accounts they're being drained and calls dump() to start draining.
  */
 /obj/structure/checkoutmachine/proc/start_dumping()
-	accounts_to_rob = flatten_list(SSeconomy.bank_accounts_by_id)
+	accounts_to_rob = assoc_to_values(SSeconomy.bank_accounts_by_id)
 	accounts_to_rob -= bogdanoff?.get_bank_account()
 	for(var/i in accounts_to_rob)
 		var/datum/bank_account/B = i