PCI: endpoint: pci-epf-ntb: Remove duplicate resource teardown

In the Linux kernel, the following vulnerability has been resolved: PCI: endpoint: pci-epf-ntb: Remove duplicate resource teardown epf_ntb_epc_destroy() duplicates the teardown that the caller is supposed to do later. This leads to an oops when .allow_link fails or when .drop_link is performed. Remove the helper. Also drop pci_epc_put(). EPC device refcounting is tied to configfs EPC group lifetime, and pci_epc_put() in the .drop_link path is sufficient.