don't explicitly include subpackage configs in export files

This reverts commit 4f36e2c793d9afd342d876600c665540c5d28ee9.

Explicitly including the subpackages' configurations isn't necessary anymore
since commit 56a93b120a65771b03b08f702f0fe6331db7aec2 which added inclusion of
*dependent* packages. Since a package always depends on its subpackages, the
functionality remains the same.