Add MobileError-related labels

This function is called from a few different places in the mobile code,
including from one special that is only executed when the
BattleTowerRoomMenu special returns with a non-zero code.

Since that special causes a blue "error" screen to appear, that looks
the exact same as the one you'd get when trying to connect from the
mobile trade corner/battle colosseum in a Pokémon Center's top floor,
and this function contains a bunch of japanese strings in a jumptable, I
think it's reasonable to assume it should be called
"DisplayMobileError".

maps/BattleTower1F.asm

@@ -91,7 +91,7 @@ Script_ChooseChallenge: ; 0x9e40f
 	special BattleTowerAction
 	special BattleTowerRoomMenu
 	if_equal $a, Script_Menu_ChallengeExplanationCancel
-	if_not_equal $0, UnknownScript_0x9e550
+	if_not_equal $0, Script_MobileError
 	writebyte BATTLETOWERACTION_11
 	special BattleTowerAction
 	writetext Text_RightThisWayToYourBattleRoom
@@ -159,7 +159,7 @@ Script_BattleTowerHopeToServeYouAgain:
 	end
 
 UnreferencedScript_0x9e4b6:
-	special Function17f53d
+	special BattleTowerMobileError
 	closetext
 	end
 
@@ -178,7 +178,7 @@ UnreferencedScript_0x9e4be:
 	special BattleTowerAction
 	special Function1700ba
 	if_equal $a, Script_Menu_ChallengeExplanationCancel
-	if_not_equal $0, UnknownScript_0x9e550
+	if_not_equal $0, Script_MobileError
 	writetext Text_ReceivedAListOfLeadersOnTheHonorRoll
 	spriteface BATTLETOWER1F_RECEPTIONIST, LEFT
 	writetext Text_PleaseConfirmOnThisMonitor
@@ -237,8 +237,8 @@ Script_MayNotEnterABattleRoomUnderL70: ; 0x9e549
 	waitbutton
 	jump Script_Menu_ChallengeExplanationCancel
 
-UnknownScript_0x9e550:
-	special Function17f53d
+Script_MobileError:
+	special BattleTowerMobileError
 	closetext
 	end