chore: update flatpak install

tidy and remove Slack

Containerfile

@@ -16,10 +16,7 @@ RUN sed -i -e '0,/enabled=0/s//enabled=1/' /etc/yum.repos.d/fedora-updates-testi
 RUN bootupctl backend generate-update-metadata && \
   echo -e '\n\nii ALL=(ALL) NOPASSWD:ALL\n\n' >> /etc/sudoers
 RUN flatpak remote-add --installation=image --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo && \
-  flatpak install --installation=image -y org.mozilla.firefox && \
-  flatpak install --installation=image -y com.slack.Slack && \
-  flatpak install --installation=image -y net.sonic_pi.SonicPi && \
-  flatpak install --installation=image -y edu.mit.Scratch
+  flatpak install --installation=image -y org.mozilla.firefox net.sonic_pi.SonicPi edu.mit.Scratch
 COPY cosign.pub /usr/etc/pki/containers/ii.pub
 RUN rm -fr /tmp/* /var/* \
     && ostree container commit