Remove the remaining fee estimation globals

This moves the CBlockPolicyEstimator to the NodeContext, which get rids
of two globals and allows us to conditionally create the
CBlockPolicyEstimator (and to remove a circular dep).

Signed-off-by: Antoine Poinsot <darosior@protonmail.com>

src/node/context.h

@@ -12,6 +12,7 @@
 
 class ArgsManager;
 class BanMan;
+class CBlockPolicyEstimator;
 class CConnman;
 class CScheduler;
 class CTxMemPool;
@@ -36,6 +37,7 @@ class WalletClient;
 struct NodeContext {
     std::unique_ptr<CConnman> connman;
     std::unique_ptr<CTxMemPool> mempool;
+    std::unique_ptr<CBlockPolicyEstimator> fee_estimator;
     std::unique_ptr<PeerManager> peerman;
     ChainstateManager* chainman{nullptr}; // Currently a raw pointer because the memory is not managed by this struct
     std::unique_ptr<BanMan> banman;