ramips: remove factory image for TP-Link Archer C2 v1

Initial commit 8375623a0640 ("ramips: add support for TP-Link Archer
C2") contains detailed installation instructions, which do not mention
a factory image. From what I can see, no support to install OpenWrt
through the vendor web interface has been added since. The factory
image is also conspicuously absent from the device page in the wiki.
Yet, it is available for download.

I bricked my Archer C2 loading the factory image through the web UI.
Serial showed this error during bootloop:

  Uncompressing Kernel Image ... LZMA ERROR 1 - must RESET board to recover

This patch disables the undocumented factory image so users won't get
tricked into thinking easy web UI flashing actually works.

Signed-off-by: Stijn Segers <[email protected]>

target/linux/ramips/image/mt7620.mk

@@ -996,6 +996,7 @@ define Device/tplink_archer-c2-v1
   TPLINK_FLASHLAYOUT := 8Mmtk
   TPLINK_HWID := 0xc7500001
   TPLINK_HWREV := 50
+  IMAGES := sysupgrade.bin
   DEVICE_MODEL := Archer C2
   DEVICE_VARIANT := v1
   DEVICE_PACKAGES := kmod-mt76x0e kmod-usb2 kmod-usb-ohci \