test: Replace importprivkey with wallet_importprivkey

importprivkey was a legacy wallet only RPC which had a helper for
descriptor wallets in tests. Add wallet_importprivkey helper and use it
wherever importprivkey is used (other than backward compatibility tests)

test/functional/wallet_hd.py

@@ -10,6 +10,7 @@ from test_framework.blocktools import COINBASE_MATURITY
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
+    wallet_importprivkey,
 )
 
 
@@ -39,7 +40,7 @@ class WalletHDTest(BitcoinTestFramework):
         # Import a non-HD private key in the HD wallet
         non_hd_add = 'bcrt1qmevj8zfx0wdvp05cqwkmr6mxkfx60yezwjksmt'
         non_hd_key = 'cS9umN9w6cDMuRVYdbkfE4c7YUFLJRoXMfhQ569uY4odiQbVN8Rt'
-        self.nodes[1].importprivkey(non_hd_key)
+        wallet_importprivkey(self.nodes[1], non_hd_key, "now")
 
         # This should be enough to keep the master key and the non-HD key
         self.nodes[1].backupwallet(self.nodes[1].datadir_path / "hd.bak")