docs: driver-api: address duplicate label warning

Delete identically named subsection to fix Documentation warning:

  Documentation/driver-api/w1.rst:11: \
  WARNING: duplicate label driver-api/w1:w1 api internal to the kernel, \
  other instance in Documentation/driver-api/w1.rst

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20200330060132.7773-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/w1.rst

@@ -7,9 +7,6 @@ W1: Dallas' 1-wire bus
 W1 API internal to the kernel
 =============================
 
-W1 API internal to the kernel
------------------------------
-
 include/linux/w1.h
 ~~~~~~~~~~~~~~~~~~