fix: prevent delete from sending multiple args in callback

ci/Jenkinsfile

@@ -1,2 +1,2 @@
 // Warning: This file is automatically synced from https://github.com/ipfs/ci-sync so if you want to change it, please change it there and ask someone to sync all repositories.
-javascript()
+javascript(['nodejs_versions': ['8.11.1','9.2.0','10.0.0']])

src/index.js

@@ -225,7 +225,10 @@ class FsDatastore {
    */
   delete (key /* : Key */, callback /* : Callback<void> */) /* : void */ {
     const parts = this._encode(key)
-    fs.unlink(parts.file, callback)
+    fs.unlink(parts.file, (err) => {
+      // Avoid injection of additional params, we only need the error
+      callback(err)
+    })
   }
 
   /**