This commit changes the logic of the code that builds the queries for
the 'used shipping method' filter. The initial implementation relied
only on the shipping method name that is stored in
wp_woocommerce_order_items. This implementation did not work as the
name is not unique. The new implementation use the shipping method id
and the instance id that are stored in wp_woocommerce_order_itemmeta and
the combination of both fields is unique.
[MAILPOET-4992]
f20878f7f3