Fix nested columns constant

[FelipeSBarros]

@cuducos , during the construction of the flatten function I have wrongly added some "column name" (dict keys, for now) in the NESTED_COLUMNS constant.

I did it by reading the API documentation. But once finished the PR #100 I did some test with real data an realized that some "columns" are not nested. I created a issue #101 about it. (sorry, I should have tested before closing the PR... I will try to be more careful next time)

Today I fixed it removing those "columns names" and added some other. This time I have tested with occurrences from the second semester of 2022.

from crossfire import AsyncClient, flatten

client = AsyncClient()
states_dict, _ = await client.states(format="dict")
states_df, _ = await client.states(format="df")

cities_rj, _ = await client.cities(state_id=states_df.id.iloc[0], format="df")

occs = await client.occurrences(
    id_state=cities_rj.state.iloc[16].get("id"),
    id_cities=cities_rj.id.iloc[16],
    initial_date="2022-06-01",
    final_date="2023-01-01",
    # format="df",
)

flatten(occs)

Everythning seems to be right.