[bugfix] bad index for removeAt

Now, the removal is done with array's reference comparison with
mu.list.remove instead of using an index with mu.list.removeAt
because the index needs to be updated when a character is removed

Since characters contain a property with its position, the character
and map models does not have to be related with a property in the
database models. The relation can be performed with reference
comparisson in the client and updated when new data comes from the
backend

Since each push from the backend will generate a new array reference,
is needed to update both, character and map models with the new
reference in order to success with the reference comparissons