ldpd: remove pseudowire LSP check

ldpd: remove pseudowire LSP check

In order to bring a pseudowire up, we must make sure that there's at
least one LSP available to its remote end (otherwise the labeled frames
from the CEs wouldn't reach their destination). We were doing this
check in ldpd, but doing so is very limiting because it doesn't consider
other types of LSPs that might be available (static LSPs, RSVP-TE, SR,
etc). Thus remove this check from the l2vpn_pw_ok() function. Later
on we'll implement a pseudowire manager in zebra which will solve this
problem in a much better way (including notifying ldpd about failures
to install a pseudowire in the kernel/hardware).

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