ldpd: remove a few unnecessary functions

ldpd: remove a few unnecessary functions

The original ldpd(8) daemon in OpenBSD doesn't allow the user to put
non-existing interfaces in the configuration file. For this reason,
the l2vpn_if_find() and l2vpn_pw_find() functions take an ifindex as
an argument.  In FRR's ldpd we can put non-existing interfaces in the
configuration, and they are activated as soon as they are available. For
this reason, we can't lookup interfaces by their ifindex in this port.
The l2vpn_if_find_name() and l2vpn_pw_find_name() functions were
introduced to address this issue. However, since the "find-by-ifindex"
functions are not being used anymore, we can just remove them and rename
the *_find_name() functions removing the "_name" suffix.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>