Update Dockerfiles to install Python deps from PyPI as per deploy docs.

Dockerfile-debian-11-sqlite

@@ -66,16 +66,15 @@ virtualenv
 
 # Install make and runtime dependencies.
 #
-# Excluding python3-celery here due to conflict with dist-packges for a
-# compatible version of billiard.
-# TODO: Align with deploying docs.
+# We explicitly don't use use Debian packages for everything here, so as to
+# match closely with the deployment docs which install most depedencies
+# from PyPI.
 RUN apt-get install -y \
-python3-alembic \
-python3-feedgenerator \
-python3-jsonschema \
 python3-lxml \
-python3-migrate \
-python3-py \
+python3-pil
+
+# Install test and docs dependencies.
+RUN apt-get install -y \
 python3-pytest \
 python3-pytest-xdist \
 python3-snowballstemmer \

Dockerfile-fedora-33-sqlite

@@ -22,26 +22,20 @@ virtualenv
 
 RUN dnf -y install \
 findutils \
-python3-alembic \
-python3-celery \
-python3-feedgenerator \
-python3-jsonschema \
+# To build waitress on Fedora 33 (not required for 31)
+libffi-devel \
 python3-lxml \
-python3-migrate \
-# Fedora only
 python3-pillow \
-python3-py \
+which
+
+RUN dnf -y install \
 python3-pytest \
 python3-pytest-xdist \
 python3-snowballstemmer \
 python3-sphinx \
 # Not in Fedora
 # python3-sphinxcontrib.websupport \
-python3-webtest \
-# Fedora only
-which \
-# To build waitress on Fedora 33 (not required for 31)
-libffi-devel
+python3-webtest
 
 RUN dnf -y install \
 gstreamer1-plugins-base \