Nuke the Teklia CA certificate

Before we rewrote the Arkindex dev setup, we had to use a custom certification authority to generate certificates for ark.localhost, and this CA had to be added to anything that might be run on a development Arkindex instance. arkindex/backend!2251 (merged) removed this, and tools/python-toolbox!13 (merged) adds a different hack instead, so the CA file should be removed from the cookiecutter template's Dockerfile.