Drop Generation.canonical_pokedex.

Generation VI doesn't have a canonical pokedex (it has three). We don't
use this anywhere and as far as i can tell we never have. We can revive
it in another form if and when we find we need it.

Conflicts:
	pokedex/data/csv/generations.csv
	pokedex/db/tables.py
Add XY region, generation, version, and dex names.