Remove the extensions/chromium/.eslintrc file (PR 19029 follow-up)

This file became unused in PR 19029, but we apparently forgot to remove it.

extensions/chromium/.eslintrc

@@ -1,36 +0,0 @@
-{
-  "extends": [
-    ../../.eslintrc
-  ],
-
-  "env": {
-    "webextensions": true
-  },
-
-  "parserOptions": {
-    "sourceType": "script"
-  },
-
-  "rules": {
-    "no-var": "off",
-  },
-
-  "overrides": [
-    {
-      // Include all files referenced in background.js
-      "files": [
-        "options/migration.js",
-        "preserve-referer.js",
-        "pdfHandler.js",
-        "extension-router.js",
-        "suppress-update.js",
-        "telemetry.js"
-      ],
-      "env": {
-        // Background script is a service worker.
-        "browser": false,
-        "serviceworker": true
-      }
-    }
-  ]
-}