removed duplicate entry

Former-commit-id: 81327ccfc159dadb4b5efee9044b6c901b019c99

manifest.json

@@ -57,7 +57,6 @@
 			"extension/lib/single-file/index.js",
 			"extension/core/index.js",
 			"extension/ui/index.js",
-			"extension/lib/single-file/index.js",
 			"extension/lib/single-file/browser-polyfill/chrome-browser-polyfill.js",
 			"lib/single-file/vendor/css-minifier.js",
 			"lib/single-file/vendor/css-tree.js",