Don't print error code in UI error messages

It's always -1 now, so providing it is pointless.

src/gui/html/js/query.js

@@ -22,7 +22,7 @@
       persistent: false,
       onSuccess: resolve,
       onFailure: (errorCode, errorMessage) => {
-        reject(new Error(`Error code: ${errorCode}; ${errorMessage}`));
+        reject(new Error(errorMessage));
       },
     });
   });

src/tests/gui/html/js/test_query.js

@@ -34,6 +34,6 @@ describe('query()', () => {
   );
 
   it('should fail with an Error object when an error occurs', () =>
-    loot.query('fail').should.be.rejectedWith(Error, { message: 'Error code: -1; {"name":"fail","args":[]}' })
+    loot.query('fail').should.be.rejectedWith(Error, { message: '{"name":"fail","args":[]}' })
   );
 });