Check if WC_Facebookcommerce_Info_Banner is used, and possibly delete if we really don't need it.

[budzanowski]

I suspect that the class WC_Facebookcommerce_Info_Banner is not used at all.
I suspect this because the logic that triggers the use of the banner class relies on
get_external_merchant_settings_id function that gets the OPTION_EXTERNAL_MERCHANT_SETTINGS_ID option.
From what I could find this option is never set, except for some old plugin version update code.

We need to verify if this is really not used. If it is not we should check if we maybe should use it.
I don't really know what an External Merchant Settings ID is.
If we don't need it we should remove all of the class code and the code and the code that refers to OPTION_EXTERNAL_MERCHANT_SETTINGS_ID in any way.

[haszari]

We need to verify if this is really not used. If it is not we should check if we maybe should use it.

Sounds like a low priority, but if we want more data to confirm this is unused, we might be able to add tracking for the relevant settings. Probably overkill to add tracking, but thought I'd mention it.