Remove obsolete configuration and dependencies.

package.json

@@ -17,8 +17,6 @@
     "@bauke/stylelint-config": "^0.1.2",
     "@types/node": "^18.15.11",
     "@types/webextension-polyfill": "^0.10.0",
-    "ava": "^5.2.0",
-    "c8": "^7.13.0",
     "concurrently": "^8.0.1",
     "cssnano": "^6.0.0",
     "esbuild": "^0.17.15",
@@ -29,48 +27,16 @@
     "stylelint": "^15.3.0",
     "stylelint-config-standard-scss": "^7.0.1",
     "trash-cli": "^5.0.0",
-    "ts-node": "^10.9.1",
     "tsx": "^3.12.6",
     "typescript": "^5.0.2",
     "web-ext": "^7.6.0",
     "xo": "^0.53.1"
   },
-  "ava": {
-    "extensions": {
-      "ts": "module"
-    },
-    "files": [
-      "tests/**/*.test.ts"
-    ],
-    "nodeArguments": [
-      "--loader=ts-node/esm"
-    ],
-    "snapshotDir": "tests/snapshots"
-  },
-  "c8": {
-    "include": [
-      "source",
-      "tests"
-    ],
-    "reportDir": "coverage",
-    "reporter": [
-      "text",
-      "html"
-    ]
-  },
   "prettier": "@bauke/prettier-config",
   "stylelint": {
     "extends": "@bauke/stylelint-config"
   },
   "xo": {
-    "overrides": [
-      {
-        "files": "tests/**/*.test.ts",
-        "rules": {
-          "@typescript-eslint/triple-slash-reference": "off"
-        }
-      }
-    ],
     "extends": "@bauke/eslint-config",
     "prettier": true,
     "rules": {