Do not use blanket impls when building for c_bindings

The C bindings generator isn't capable of figuring out if a blanket
impl applies in a given context, and instead opts to always write
out any relevant impl's for a trait. Thus, blanket impls should be
disabled when building with `#[cfg(c_bindings)]`.

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -162,6 +162,7 @@ pub trait LockableScore<'a> {
 /// use the Persister to persist it.
 pub trait WriteableScore<'a>: LockableScore<'a> + Writeable {}
 
+#[cfg(not(c_bindings))]
 impl<'a, T> WriteableScore<'a> for T where T: LockableScore<'a> + Writeable {}
 
 /// (C-not exported)