Move lightning-custom-message to main workspace

Since we now have a consistent MSRV and edition, we can move
`lightning-custom-message` to the main
workspace.

Author: tnull

Cargo.toml

@@ -8,11 +8,11 @@ members = [
     "lightning-net-tokio",
     "lightning-persister",
     "lightning-background-processor",
-    "lightning-rapid-gossip-sync"
+    "lightning-rapid-gossip-sync",
+    "lightning-custom-message",
 ]
 
 exclude = [
-    "lightning-custom-message",
     "lightning-transaction-sync",
     "no-std-check",
     "msrv-no-dev-deps-check",

msrv-no-dev-deps-check/Cargo.toml

@@ -11,3 +11,4 @@ lightning-net-tokio = { path = "../lightning-net-tokio" }
 lightning-persister = { path = "../lightning-persister" }
 lightning-background-processor = { path = "../lightning-background-processor", features = ["futures"] }
 lightning-rapid-gossip-sync = { path = "../lightning-rapid-gossip-sync" }
+lightning-custom-message = { path = "../lightning-custom-message" }