[8.0] invoicing_voucher_killer

This module is migrated from OCA/bank-statement-reconcile 7.0.

As it's purpose is to remove the Pay buttons from the invoice forms, it is related to payment. 
This bank-payment repository is therefore a better place for it.

Since bank statements do not use vouchers in 8.0, this module is even more useful than in 7.0.

The module migrates trivally from 7.0.