chore: remove pointless dockerfile template

Noticed in #12063 - it serves no paractical use.
Developers should use the devcontainer instead.

docker/Dockerfile.develop

@@ -1,10 +0,0 @@
-FROM freqtradeorg/freqtrade:develop
-
-# Install dependencies
-COPY requirements-dev.txt /freqtrade/
-
-RUN pip install numpy --user --no-cache-dir \
-  && pip install -r requirements-dev.txt --user --no-cache-dir
-
-# Empty the ENTRYPOINT to allow all commands
-ENTRYPOINT []