cmd/govulncheck: remove unused fixup

Change-Id: I465ad24e69cb77daa19b01b3dc9cf307ce300a57
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/621597
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

cmd/govulncheck/testdata/common/config.json

@@ -43,10 +43,6 @@
     {
       "pattern": "path\": \"stdlib\",\n *\"version\": \"[^\\s]*\"",
       "replace": "path\": \"stdlib\",\n        \"version\": \"v1.18.0\""
-    },
-    {
-      "pattern": "library @ go[^\\s]*:",
-      "replace": "library @ go1.18:"
     }
   ]
 }