Re-add optional std feature dependencies to fix RGS builds

We previously removed these, leading to failure to build under default
features including `std`.

lightning-rapid-gossip-sync/Cargo.toml

@@ -11,7 +11,7 @@ Utility to process gossip routing data from Rapid Gossip Sync Server.
 
 [features]
 default = ["std"]
-std = []
+std = ["bitcoin/std", "lightning/std"]
 
 [dependencies]
 lightning = { version = "0.0.124", path = "../lightning", default-features = false }