Updates space verification unit test to use new proc (#73322)

## About The Pull Request

At San's request, updates the space verification unit test to use the
new "are we a planetary map" proc instead of having its own
implementation of the same thing.

## Why It's Good For The Game

If it gets broken in one place it will break in all of them, most
importantly the unit test, which is what we want because that's what the
test is for.

## Changelog

Not player facing.

code/modules/unit_tests/mapload_space_verification.dm

@@ -5,11 +5,8 @@
 	priority = TEST_LONGER
 
 /datum/unit_test/mapload_space_verification/Run()
-	// Get the datum associated with our currently running map.
-	var/datum/map_config/current_map = SSmapping.config
-
 	// Is our current map a planetary station (NO space turfs allowed)? If so, check for ANY space turfs.
-	if(current_map.planetary)
+	if(SSmapping.is_planetary())
 		validate_planetary_map()
 		return