Simplify Object.fromEntries usage a tiny bit in the web/generic_signature_storage.js file

As can be seen [at MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries#parameters) the `Object.fromEntries` method accepts a `Map` directly, hence using the `Map.prototype.entries` method is superfluous here.

Author: Snuffleupagus

web/generic_signature_storage.js

@@ -36,7 +36,7 @@ class SignatureStorage {
   #save() {
     localStorage.setItem(
       KEY_STORAGE,
-      JSON.stringify(Object.fromEntries(this.#signatures.entries()))
+      JSON.stringify(Object.fromEntries(this.#signatures))
     );
   }