chore: remove unused c8 (#1928)

Author: noritaka1166

package-lock.json

@@ -72,7 +72,6 @@
     "@vitest/coverage-v8": "^3.2.4",
     "@wdio/eslint": "^0.1.1",
     "@wdio/types": "^9.15.0",
-    "c8": "^10.1.3",
     "eslint": "^9.29.0",
     "husky": "^9.1.7",
     "npm-run-all2": "^8.0.4",