webmap is now in maps.txt instead of a config entry (#90821)

## About The Pull Request

Currently the button to open a map in webmap is tied to a config entry,
which would then take the name of the map being played and get the link
to that, however for cases like new/tested/admin uploaded maps where
there is no webmap available, this would still have a link to a url that
doesn't exist.
Instead, we'll make the webmap link be in ``maps.txt``, same as
feedbacklink.

## Why It's Good For The Game

Explained in the about section, this prevents webmaps appearing for maps
that aren't supposed to have a webmap link available.

## Changelog

Nothing player-facing, webmaps aren't currently used (afaik) currently
cause they're broken for tg codebases.

code/controllers/configuration/configuration.dm

@@ -435,6 +435,9 @@ Example config:
 			if("feedbacklink")
 				if(currentmap.map_name == SSmapping.current_map.map_name)
 					SSmapping.current_map.feedback_link = data
+			if("webmap_url")
+				if(currentmap.map_name == SSmapping.current_map.map_name)
+					SSmapping.current_map.mapping_url = data
 			else
 				log_config("Unknown command in map vote config: '[command]'")
 

code/controllers/configuration/entries/general.dm

@@ -785,7 +785,3 @@
 
 // If set, enables the "Link forum account" OOC verb
 /datum/config_entry/string/forum_link_uri
-
-/datum/config_entry/string/webmap_url
-	//ex: "https://webmap.affectedarc07.co.uk/maps/tgstation/"
-	default = ""

code/controllers/subsystem/mapping.dm

@@ -106,9 +106,6 @@ SUBSYSTEM_DEF(mapping)
 		if(!current_map || current_map.defaulted)
 			to_chat(world, span_boldannounce("Unable to load next or default map config, defaulting to [old_config.map_name]."))
 			current_map = old_config
-	var/mapping_url = config.Get(/datum/config_entry/string/webmap_url)
-	if(mapping_url != "")
-		current_map.mapping_url = mapping_url
 	plane_offset_to_true = list()
 	true_to_offset_planes = list()
 	plane_to_offset = list()