PCI/ERR: Remove remnants of .link_reset() callback

Back in 2017, commit 2fd260f0 ("PCI/AER: Remove unused .link_reset()
callback") removed .link_reset() from struct pci_error_handlers, but left
a few code comments behind which still mention it.  Remove them.

The code comments in the SolarFlare Ethernet drivers point out that no
.mmio_enabled() callback is needed because the driver's .error_detected()
callback always returns PCI_ERS_RESULT_NEED_RESET, which causes
pcie_do_recovery() to skip .mmio_enabled().  That's not quite correct
because efx_io_error_detected() does return PCI_ERS_RESULT_RECOVERED under
certain conditions and then .mmio_enabled() would indeed be called if it
were implemented.  Remove this misleading portion of the code comment as
well.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/1d72a891a7f57115e78a73046e776f7e0c8cd68f.1755008151.git.lukas@wunner.de