tools: docs: parse_data_structs.py: drop contents header

tools: docs: parse_data_structs.py: drop contents header

When used in practice, one may want to have multiple header
files on a single rst file, like:

	***********************
	Digital TV uAPI symbols
	***********************

	.. contents:: Table of Contents
	   :depth: 2
	   :local:

	Frontend
	========

	.. kernel-include:: include/uapi/linux/dvb/frontend.h
	    :generate-cross-refs:
	    :toc:

	Demux
	=====

	.. kernel-include:: include/uapi/linux/dvb/dmx.h
	    :generate-cross-refs:
	    :toc:

	...

So, don't add ..contents:: here.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <4bf353e5248133a3b0abd82519a38453402fe7c6.1759329363.git.mchehab+huawei@kernel.org>