Icon clean up.

devtools/background.js

@@ -48,9 +48,6 @@ chrome.runtime.onMessage.addListener( ( message, sender, sendResponse ) => {
 
 		chrome.action.setIcon( {
 			path: {
-				16: `icons/16-${message.scheme}.png`,
-				32: `icons/32-${message.scheme}.png`,
-				48: `icons/48-${message.scheme}.png`,
 				128: `icons/128-${message.scheme}.png`
 			}
 		} );

devtools/manifest.json

@@ -4,9 +4,6 @@
 	"version": "1.6",
 	"description": "Developer tools extension for Three.js",
 	"icons": {
-		"16": "icons/16-light.png",
-		"32": "icons/32-light.png",
-		"48": "icons/48-light.png",
 		"128": "icons/128-light.png"
 	},
 	"action": {},