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/validation.cpp

@@ -22,7 +22,6 @@
 #include <logging/timer.h>
 #include <node/ui_interface.h>
 #include <optional.h>
-#include <policy/fees.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
 #include <pow.h>
@@ -148,8 +147,6 @@ arith_uint256 nMinimumChainWork;
 
 CFeeRate minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
 
-CBlockPolicyEstimator feeEstimator;
-
 // Internal stuff
 namespace {
     CBlockIndex* pindexBestInvalid = nullptr;