phone: Don't save .dng files

Not needed since pictures taken with the camera are rare anyway and
I don't think using the .dng files would produce much better results.

hosts/phone/configuration.nix

@@ -134,6 +134,10 @@ in
           show-battery-percentage = true;
         };
 
+        "org/postmarketos/megapixels" = {
+          save-raw = false;
+        };
+
         "org/gnome/desktop/session" = {
           idle-delay = mkUint32 60;
         };