Revert "feature: make gossip queries compulsory"

This reverts commit 717facc202.

It turns out that we can't do this since it would result in
incompatibility with LDK. The spec has been updated to reallow
optional gossip queries so we revert this commit.

feature/default_sets.go

@@ -14,7 +14,7 @@ var defaultSetDesc = setDesc{
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},
-	lnwire.GossipQueriesRequired: {
+	lnwire.GossipQueriesOptional: {
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},