Clear armor lamp overlays (#7191)

# About the pull request

Before adding a new armor lamp overlay, remove the old one.

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# Explain why it's good for the game

Potentially infinitely stacking overlays bad.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Master, toggling lamp 10x:

![image](https://github.com/user-attachments/assets/4af9239c-01a3-4227-8fca-e97eb250d0d8)

PR, toggling lamp 10x:

![image](https://github.com/user-attachments/assets/2780a33b-6eed-4c7d-a20f-f3bf798ad20d)

</details>


# Changelog
No player facing changes.

code/modules/clothing/suits/marine_armor/_marine_armor.dm

@@ -137,6 +137,7 @@
 
 /obj/item/clothing/suit/storage/marine/update_icon(mob/user)
 	var/image/I
+	overlays -= armor_overlays["lamp"]
 	armor_overlays["lamp"] = null
 	if(flags_marine_armor & ARMOR_LAMP_OVERLAY)
 		if(flags_marine_armor & ARMOR_LAMP_ON)