Remove entity information from {civ}.json files

As of r24492 (rP24492), the civinfo page no longer reads information about
Heroes and Special Structures/Technologies from the {civ}.json files, but
from relevant templates.

Nothing else uses the entity/tech descriptive information contained in the
{civ}.json files, so we can safely remove it.

Note: The Team and Civilisation Bonus information contained within the

`{civ}.json` files are not touched in this commit.