Merge #18766: Disable fee estimation in blocksonly mode (by removing the fee estimates global)

4e28753f60 feestimator: encapsulate estimation file logic (Antoine Poinsot)
e8ea6ad9c1 init: don't create a CBlockPolicyEstimator if we don't relay transactions (Antoine Poinsot)
86ff2cf202 Remove the remaining fee estimation globals (Antoine Poinsot)
03bfeee957 interface: remove unused estimateSmartFee method from node (Antoine Poinsot)

Pull request description:

  If the `blocksonly` mode is turned on after running with transaction
  relay enabled for a while, the fee estimation will serve outdated data
  to both the internal wallet and to external applications that might be
  feerate-sensitive and make use of `estimatesmartfee` (for example a
  Lightning Network node).

  This has already caused issues (for example https://github.com/bitcoin/bitcoin/issues/16840 (C-lightning), or https://github.com/lightningnetwork/lnd/issues/2562 (LND)) and it seems prudent to fail rather than to give inaccurate values.

  This fixes #16840, and closes #16890 which tried to fix the symptoms (RPC) but not the cause as mentioned by sdaftuar :
  > If this is a substantial problem, then I would think we should take action to protect our own wallet users as well (rather than hide the results of what our fee estimation would do!).

ACKs for top commit:
  MarcoFalke:
    re-ACK 4e28753f60 👋
  jnewbery:
    utACK 4e28753f60

Tree-SHA512: c869cf03b86d8194002970bbc84662dae76874967949b9be0d9a4511a1eabcb1627c38aca3154da9dcece1a4c49ec02bd4f9fcca2ec310986e07904559e63ba8

test/functional/feature_fee_estimation.py

@@ -13,6 +13,7 @@ from test_framework.util import (
     assert_equal,
     assert_greater_than,
     assert_greater_than_or_equal,
+    assert_raises_rpc_error,
     satoshi_round,
 )
 
@@ -262,6 +263,11 @@ class EstimateFeeTest(BitcoinTestFramework):
         self.log.info("Final estimates after emptying mempools")
         check_estimates(self.nodes[1], self.fees_per_kb)
 
+        self.log.info("Testing that fee estimation is disabled in blocksonly.")
+        self.restart_node(0, ["-blocksonly"])
+        assert_raises_rpc_error(-32603, "Fee estimation disabled",
+                                self.nodes[0].estimatesmartfee, 2)
+
 
 if __name__ == '__main__':
     EstimateFeeTest().main()

test/lint/lint-circular-dependencies.sh

@@ -20,7 +20,6 @@ EXPECTED_CIRCULAR_DEPENDENCIES=(
     "txmempool -> validation -> txmempool"
     "wallet/fees -> wallet/wallet -> wallet/fees"
     "wallet/wallet -> wallet/walletdb -> wallet/wallet"
-    "policy/fees -> txmempool -> validation -> policy/fees"
 )
 
 EXIT_CODE=0