media: index.rst: exclude Indexes section from latex/pdf output

With LaTex, the Index at the end will always be present. Having
an extra chapter for it there will just add extra noise to the
document.
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/index.rst

@@ -18,7 +18,7 @@ Linux Media Subsystem Documentation
    v4l-drivers/index
    cec-drivers/index
 
-.. only::  subproject
+.. only:: html and subproject
 
    Indices
    =======