`transient delete --all/--expired` doesn't delete all transients

[ocean90]

To better understand the issue please take a look at core's delete_expired_transients().

There are three cases:

1. _transient_ in $wpdb->options for regular transients
2. _site_transient_ in $wpdb->options for site transients when not multisite
3. _site_transient_ in $wpdb->sitemeta for site transients when multisite

delete_expired() only handles case 1, delete_all() only case 1 and 2. Both should be updated to support all three cases by default as I don't think we should bother the user with the --network flag in this case.

Site transients are for example used for plugin/theme/available translations checks.