apm821xx: nand remove obsolete kernel config symbol

The missing CONFIG_USB_XHCI_PCI dependency on CONFIG_USB_PCI of the
µPD720201 xhci-pci(e) usb 3.0 chip used by the WNDR4700 was fixed with
6112abf186 ("kernel: enable CONFIG_USB_PCI for PCI usb modules").

Commit c38fb58576 ("kernel: fix disabling common usb quirks on 4.14")
finally fixed the following build error:

drivers/usb/host/xhci-pci.c: In function 'xhci_pci_probe':
drivers/usb/host/xhci-pci.c:749:6: error: implicit declaration of function 'usb_xhci_needs_pci_reset' [-Werror=implicit-function-declaration]
  if (usb_xhci_needs_pci_reset(dev)) {

Hence the CONFIG_USB_PCI symbol isn't required any longer in target kernel
config.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/apm821xx/nand/config-default

@@ -39,7 +39,6 @@ CONFIG_MTD_UBI_BLOCK=y
 CONFIG_MTD_UBI_WL_THRESHOLD=4096
 CONFIG_UBIFS_FS=y
 # CONFIG_UBIFS_FS_ADVANCED_COMPR is not set
-CONFIG_USB_PCI=y
 CONFIG_SENSORS_LM90=y
 CONFIG_SENSORS_TC654=y
 CONFIG_SWCONFIG=y