scripted-diff: Use wallets_path and chain_path where possible

Instead of passing the datadir and chain name to os.path.join, just use
the existing properties, which are the same.

-BEGIN VERIFY SCRIPT-
 sed -i --regexp-extended 's|\.datadir, self\.chain, .wallets.|.wallets_path|g' $(git grep -l '\.datadir, self\.chain,')
 sed -i --regexp-extended 's|\.datadir, self\.chain,|.chain_path,|g'            $(git grep -l '\.datadir, self\.chain,')
-END VERIFY SCRIPT-

test/functional/feature_fee_estimation.py

@@ -421,7 +421,7 @@ class EstimateFeeTest(BitcoinTestFramework):
 
         self.log.info("Restarting node with fresh estimation")
         self.stop_node(0)
-        fee_dat = os.path.join(self.nodes[0].datadir, self.chain, "fee_estimates.dat")
+        fee_dat = os.path.join(self.nodes[0].chain_path, "fee_estimates.dat")
         os.remove(fee_dat)
         self.start_node(0)
         self.connect_nodes(0, 1)