Remove docker/ directory (#145)

The docker/ image bundles OQS-OpenSSL so docker/minitest.py can
exercise PQ-TLS interop. But liboqs-python does not add PQ support to
Python, so there is no reason to test that here. Testing of PQ-TLS
interoperability involving oqs-provider or OQS-OpenSSL should happen
in oqs-provider or oqs-demos, not here.

The easy-onboarding use case the docker setup originally addressed is
now covered by the root Dockerfile plus liboqs-python's runtime auto-
install of liboqs. docker/Dockerfile-simple overlaps in purpose with
the root Dockerfile and isn't referenced anywhere. Thus the docker/
folder is no longer needed.

Signed-off-by: Douglas Stebila <dstebila@uwaterloo.ca>

Author: dstebila

README.md

@@ -235,9 +235,6 @@ mount your current project in the Docker container with
 docker run --rm -it --workdir=/app -v ${PWD}:/app oqs-python /bin/bash
 ```
 
-A more comprehensive Docker example is provided in the directory
-[`docker`](https://github.com/open-quantum-safe/liboqs-python/tree/main/docker).
-
 ---
 
 ## Limitations and security