doc: fix PDF build

doc: fix PDF build

The command "make doc-guides-pdf" is failing because
there are more than 1500 lines in the file MAINTAINERS
which is included in the contributing guide.

We are facing the issue mentioned in this comment:
https://github.com/sphinx-doc/sphinx/issues/3099#issuecomment-256440704

Anyway the file MAINTAINERS is mentioned several times in the guide.
So the "literalinclude" is removed from the guide to fix the build
of the PDF.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Tested-by: Ferruh Yigit <ferruh.yigit@intel.com>