As a backend developer, I want to remove unnecessary code that refers to census block groups.

[lucasmbrown-usds]

Description There is scattered code throughout the codebase that refers to census block groups. See vars like EXPECTED_CENSUS_BLOCK_GROUPS_CHARACTER_LENGTH, as well as code snippets like:

        for (
            geo_level,
            geo_field,
            expected_geo_field_characters,
            expected_rows,
        ) in [
            (
                ValidGeoLevel.CENSUS_TRACT,
                self.GEOID_TRACT_FIELD_NAME,
                self.EXPECTED_CENSUS_TRACTS_CHARACTER_LENGTH,
                self.EXPECTED_MAX_CENSUS_TRACTS,
            ),
            (
                ValidGeoLevel.CENSUS_BLOCK_GROUP,
                self.GEOID_FIELD_NAME,
                self.EXPECTED_CENSUS_BLOCK_GROUPS_CHARACTER_LENGTH,
                self.EXPECTED_MAX_CENSUS_BLOCK_GROUPS,
            ),
        ]:

With officially moving over to only supporting tracts for data sources instead of tracts and block groups, we can remove all of this old and unnecessary code about block groups.