remove curl, but not the certificates.

docker/gcc-ubuntu/Dockerfile

@@ -112,7 +112,8 @@ COPY --from=tpl_toolchain ${GEOSX_TPL_DIR} ${GEOSX_TPL_DIR}
 # Install `sccache` binaries to speed up the build of `geos`.
 RUN apt-get install -y --no-install-recommends curl ca-certificates && \
     mkdir -p /opt/sccache/bin && \
-    curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.5.4/sccache-v0.5.4-x86_64-unknown-linux-musl.tar.gz | tar --directory=/opt/sccache/bin --strip-components=1 -xzf -
+    curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.5.4/sccache-v0.5.4-x86_64-unknown-linux-musl.tar.gz | tar --directory=/opt/sccache/bin --strip-components=1 -xzf - && \
+    apt-get purge --auto-remove -y curl
 # Any tool specific to building GEOSX shall be installed in this stage.
 RUN apt-get install -y --no-install-recommends \
     openssh-client \