Fixed handling of regions to be deleted

- Merged their contents in memory into the regions that are going to replace them, before running the usual logic
- Used countryList and regionListByCountry to go through regions that have been kept (instead of locationTree) to go through empty regions and countries, too
- Removed unused code (there are no region location entries in locationTreeOld)
- Added country entry to the location table in the unit tests to trigger the bug