Remove requirement for bob.db.drishtigs1

bob/ip/binseg/configs/datasets/dristhigs1_cup.py

bob/ip/binseg/configs/datasets/dristhigs1_cup_test.py

bob/ip/binseg/configs/datasets/dristhigs1_od.py

bob/ip/binseg/configs/datasets/dristhigs1_od_test.py

bob/ip/binseg/data/drishtigs1/__init__.py

bob/ip/binseg/data/drishtigs1/optic-cup.json

bob/ip/binseg/data/drishtigs1/optic-disc.json

bob/ip/binseg/data/drishtigs1/test.py

bob/ip/binseg/test/test_config.py

conda/meta.yaml

doc/api.rst