doc: remove code from KNI example guide

doc: remove code from KNI example guide

The example code is showing how to use KNI, and can be found in
	examples/kni/
The documentation guide for this example is explaining the code
to ease the understanding of the example.
And inside this documentation, there are a lot of examples code
which are copy/pasted. It is really too much and hard to maintain.

The code inside this documentation is replaced by the name
of the functions.

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