psc-cpp-ubuntu-20.04: just do normal cmake get

Author: JamesMcClung

docker/psc-cpp-ubuntu-20.04/Dockerfile

@@ -7,16 +7,5 @@ RUN apt-get update \
     libopenmpi-dev ninja-build \
     apt-transport-https ca-certificates gnupg software-properties-common wget \
     libhdf5-openmpi-dev \
-    libadios2-mpi-c++11-dev libadios2-mpi-c-dev
-
-# cmake version 3.21 is gtensor's lower bound as of March 11 2026;
-# it would probably work just as well to use the "latest" cmake, but
-# Docker caches RUN commands and will use the cached "latest" cmake indefinitely
-RUN wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc  \
-    | gpg --dearmor - > /etc/apt/trusted.gpg.d/kitware.gpg \
-    && apt-add-repository 'deb https://apt.kitware.com/ubuntu/ noble main' \
-    && apt-get update \
-# if cmake needs to be updated, this shows the available versions:
-    # && apt-cache madison cmake \
-    && apt-get -y install --no-install-recommends cmake=4.2.3-0kitware1ubuntu20.04.1
-
+    libadios2-mpi-c++11-dev libadios2-mpi-c-dev \
+    cmake