Extra `_index` being added to dims

[jacobbieker]

Describe the bug
make_dim_index appends _index to the coordinates of a data array. This is called in multiple places, including convert_data_array_to_dataset and in create_batch for a DataSource. This results in coordinates with names such as x_index_index and data variables of x_index as well as the original x.

To Reproduce
Steps to reproduce the behavior:

1. Run the test_get_batch_2km in Topographioc data source tests and print out the resulting Batch to confirm. Same with the MetaDataDataSource.

Expected behavior
There is only 1 index coordinate.

Additional context
Found this debugging MetadataDataSource in #314 and verified it also happens to the TopographicDataSource.

[jacobbieker]

Essentially a duplicate of #318