Fix bug where map is not removing current vehicle markers not present in the new list

[DeeTheDev]

In the map, whenever we update vehicle markers, we want to do the following:

1. Add vehicle markers that are not in the current list
2. Remove:
   a. current markers that are not in the new list
   b. current out-of-bound markers that are not in the new bounds

Currently, we are not checking 2a.
As a result of not checking, old markers that are not removed from the map are still clickable and will give an error (vehicle not available) when trying to fetch the vehicle from the backend.

Fix this in frontend mapBuilder.js file.