doc: remove outdated guidelines for library addition

doc: remove outdated guidelines for library addition

There was a doc about how to extend DPDK by adding a library.
It could have been useful but was never updated,
so it is lacking a lot of explanations about doxygen,
meson, versioning, maintainership, etc.

Anyway such guidelines should fit in the contributors guide.
Better to completely remove this obsolete document.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: David Marchand <david.marchand@redhat.com>