[media] DocBook: Fix docbook compilation

changeset 1248c7cb broke html compilation:

Documentation/DocBook/v4l2.xml:584: parser error : Entity 'sub-subdev-g-edid' not defined
Documentation/DocBook/v4l2.xml:626: parser error : chunk is not well balanced
Documentation/DocBook/media_api.xml:74: parser error : Failure to process entity sub-v4l2
Documentation/DocBook/media_api.xml:74: parser error : Entity 'sub-v4l2' not defined

I suspect that one file was simply missed at the patch. Yet, keeping
it broken is a very bad idea, so we should either remove the broken
patch or to remove just the invalid include. Let's take the latter
approach.

Due to that, a warning is now produced:

Error: no ID for constraint linkend: v4l2-subdev-edid.

Cc: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>