move-mostly: Make fHavePruned a BlockMan member

[META] In the next commit, we move the clearing of fHavePruned to
       BlockManager::Unload()

src/node/interfaces.cpp

@@ -645,7 +645,7 @@ public:
     bool havePruned() override
     {
         LOCK(cs_main);
-        return node::fHavePruned;
+        return m_node.chainman->m_blockman.fHavePruned;
     }
     bool isReadyToBroadcast() override { return !node::fImporting && !node::fReindex && !isInitialBlockDownload(); }
     bool isInitialBlockDownload() override {