Issue nucivic/dkan#268 removes json name validation

This removes validation for the json name. In this commit: https://github.com/NuCivic/visualization_entity/commit/6dff056452a51cfac30e14eb9bd6566f6843a1f6 we made it possible to have a different data_column from the map_column. 

Now the map_column matches the geojson_key property in the geojson file. We are no longer using the field_name_attribute which this is checking for since that can be different depending on the data. We could have two resources:

| name | geojson_key | value |
| -------| -------| -------|
| aaron | us | awesome |
| teo | ar | the best |
| mariano | ar |  amazing |

and

| name | country_name | value |
| -------| -------| -------|
| aaron | United States | incredible |
| teo | Argentina | best ever |
| mariano | Argentina |  fantastic |

that both match up to the same geojson_file which might have property values of country_abbreviation (us, ar) and country_name (Unites States, Argentina).

### Acceptance test
- [x] Remove "name attribute" from geojson_file and create a choropleth map. "name attribute" on geojson_file should no longer be necessary.