docs: generate deltachat-rpc-client documentation

To preview the docs, run:
```
scripts/build-python-docs.sh
firefox dist/html/index.html
```

I have removed the Makefile because modern Sphinx Makefile is just a
wrapper for `sphinx-build -M`:
3596590317/sphinx/templates/quickstart/Makefile.new_t
and sphinx-quickstart even has an option `--no-makefile`.
`make.bat` makes even less sense.
In `scripts/build-python-docs.sh` I use `sphinx-build` directly
without `make` wrapper.

scripts/concourse/docs_wheels.yml

@@ -102,8 +102,6 @@ jobs:
             - name: deltachat-core-rust-release
               path: .
           outputs:
-            - name: py-docs
-              path: ./python/doc/_build/
             # Binary wheels
             - name: py-wheels
               path: ./python/.docker-tox/wheelhouse/
@@ -115,28 +113,6 @@ jobs:
               - |
                 scripts/run_all.sh
 
-      # Upload python docs to py.delta.chat
-      - task: upload-py-docs
-        config:
-          inputs:
-            - name: py-docs
-          image_resource:
-            type: registry-image
-            source:
-              repository: alpine
-          platform: linux
-          run:
-            path: sh
-            args:
-              - -ec
-              - |
-                apk add --no-cache rsync openssh-client
-                mkdir -p ~/.ssh
-                chmod 700 ~/.ssh
-                echo "(("c.delta.chat".private_key))" > ~/.ssh/id_ed25519
-                chmod 600 ~/.ssh/id_ed25519
-                rsync -e "ssh -o StrictHostKeyChecking=no" -avz --delete py-docs/html/ delta@py.delta.chat:build/master
-
       # Upload x86_64 wheels and source packages
       - task: upload-wheels
         config: