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

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: 4e17e1db9647 ("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>