wallet: rpc: deprecate removeprunedfunds

This RPC has no helpful use while being both dangerous and a maintenance
burden.

Despite what the name says, it allows the deletion of arbitrary
transactions, and `importprunedfunds` does not allow the importing of
transactions not belonging to the user, and `listtransactions` does not
list transactions not belonging to the wallet, so this RPC can only be
used to delete transactions actually belonging to the wallet, and in the
unlikely event that transactions not belonging to the wallet are
present, they cause no harm except for occupying a few bytes on the
users disk.

test/functional/rpc_deprecated.py

@@ -4,6 +4,8 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test deprecation of RPC calls."""
 from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_raises_rpc_error
+
 
 class DeprecatedRpcTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -26,7 +28,17 @@ class DeprecatedRpcTest(BitcoinTestFramework):
 
         # Please don't delete nor modify this comment
         self.log.info("Tests for deprecated RPC methods (if any)")
-        self.log.info("Currently no tests for deprecated RPC methods")
+        if self.is_wallet_compiled():
+            self.log.info("Tests for deprecated wallet-related RPC methods (if any)")
+            self.nodes[0].createwallet("ancient_wallet")
+            wallet = self.nodes[0].get_wallet_rpc("ancient_wallet")
+
+            self.log.info("Test removeprunedfunds deprecation")
+            assert_raises_rpc_error(
+                -32, "Start bitcoind with the `-deprecatedrpc=removeprunedfunds`",
+                wallet.removeprunedfunds,
+                "fakeargument"
+            )
 
 
 if __name__ == '__main__':

test/functional/wallet_importprunedfunds.py

@@ -25,6 +25,7 @@ class ImportPrunedFundsTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 2
+        self.extra_args = [["-deprecatedrpc=removeprunedfunds"]] * 2
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()