Revert everything except the pip fix and the branch flag

docker/3_buildwheels/Dockerfile

@@ -5,7 +5,6 @@ RUN set -ex; \
     apt-get update; \
     DEBIAN_FRONTEND=noninteractive apt-get install -qy \
     git \
-    rustc python3-setuptools python3-wheel python3-pip \
     build-essential \
     checkinstall \
     libffi-dev \
@@ -13,7 +12,6 @@ RUN set -ex; \
     libjpeg-dev \
     zlib1g-dev
 
-ENV CRYPTOGRAPHY_DONT_BUILD_RUST 1
 ENV WHEELHOUSE=/data/wheelhouse
 ENV PIP_WHEEL_DIR=/data/wheelhouse
 ENV PIP_FIND_LINKS=/data/wheelhouse