ltrace: Removes the libelf dependency

The libelf is currently provided by 2 packages libelf and
elfutils. The first package provides an old version of the libelf
which is no more compatible with a recent version of ltrace. This
patch removes the dependency on the libelf package and only keep the
elfuils package which provides the accurate version of libelf for
ltrace.

It will also allow to remove the libelf package and to avoid conflicts
with two packages providing the same library.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>