docs: ABI: sysfs-c2port: remove a duplicated entry

As warned by scripts/get_abi.pl:
	Warning: /sys/class/c2port/c2portX/flash_erase is defined 2 times:  Documentation/ABI/testing/sysfs-c2port:60  Documentation/ABI/testing/sysfs-c2port:68

This entry was added twice at the same patch. Probalby a
cut-and paste issue.

Fixes: 4e17e1d ("Add c2 port support")
Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/4ea2b31ddc76161fbae004f2f2ed91dfb757703f.1604042072.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: mchehab

Documentation/ABI/testing/sysfs-c2port

@@ -66,13 +66,6 @@ Description:
 		the "erase" command on the on-board flash of the connected
 		micro.
 
-What:		/sys/class/c2port/c2portX/flash_erase
-Date:		October 2008
-Contact:	Rodolfo Giometti <giometti@linux.it>
-Description:
-		The /sys/class/c2port/c2portX/flash_erase file show the
-		on-board flash size of the connected micro.
-
 What:		/sys/class/c2port/c2portX/reset
 Date:		October 2008
 Contact:	Rodolfo Giometti <giometti@linux.it>