init refactor: Remove node.init accesss in AppInitInterfaces

There's no change in behavior. This is just a refactoring to avoid a minor
layer violation in init code. The node.init object is intended to return
interface pointers for code outside the node (like wallet and gui code), not
used by node itself to initialize its internal state.

(Motivation for this change is to introduce a MakeMining wait_loaded option in
an upcoming commit that can only be used internally and not set by external
clients.)

src/init.cpp

@@ -1206,8 +1206,8 @@ bool AppInitLockDirectories()
 
 bool AppInitInterfaces(NodeContext& node)
 {
-    node.chain = node.init->makeChain();
-    node.mining = node.init->makeMining();
+    node.chain = interfaces::MakeChain(node);
+    node.mining = interfaces::MakeMining(node);
     return true;
 }