Don't specify packing properties for internal children.
This doesn't work unless the internal children are actually
direct children of the container (which we are about to
change for GtkInfoBar). Also, it is redundant, since we
just set the properties to the values they already have
anyway.
Having the changes for composite widget templates makes it impossible
to merge the places-sidebar branch. So, we will merge that branch,
and *then* apply the changes for composite templates.
This reverts commit bf909f5615.
