Deletes area var on clients (#80037)

## About The Pull Request

Literally nothing wrote to or accessed this variable, in pretty much
_every_ case we just use `get_area(mob)` instead of ever looking at the
client's area (again, ???)
## Why It's Good For The Game

this variable was added 12 years ago and I don't think anyone has ever
novelly used this.
## Changelog
Doesn't matter to players.

code/modules/client/client_defines.dm

@@ -76,8 +76,6 @@
 	var/move_delay = 0
 	///The visual delay to use for the current client.Move(), mostly used for making a client based move look like it came from some other slower source
 	var/visual_delay = 0
-	///Current area of the controlled mob
-	var/area = null
 
 		///////////////
 		//SOUND STUFF//