gnome-base: Switch back to gnome-software

Byzantium does not have PureOS Store yet

gnome-base-all

@@ -7,6 +7,8 @@ gnome-initial-setup
 gnome-online-accounts
 gnome-session-bin
 gnome-settings-daemon
+gnome-software
+gnome-software-plugin-flatpak
 gstreamer1.0-libav
 gstreamer1.0-packagekit
 gvfs-backends
@@ -15,8 +17,6 @@ network-manager-gnome
 phoc
 phosh
 phosh-mobile-tweaks
-pureos-store
-pureos-store-plugin-flatpak
 sound-theme-librem5
 squeekboard
 udisks2