[feature] make FeatureEdge no longer Eq, PartialEq or Hash

This is because we're going to replace the Dependency enum's variants with
TargetPredicates, which don't implement any of those.

We may reintroduce this in the future if necessary.

guppy/src/graph/feature/graph_impl.rs

@@ -444,7 +444,7 @@ impl FeatureNode {
 }
 
 /// Information about why a feature depends on another feature.
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Debug)]
 pub(in crate::graph) enum FeatureEdge {
     /// This edge is from a feature to its base package.
     FeatureToBase,