rpc: Optimize serialization disk space of dumptxoutset

Co-authored-by: Aurèle Oulès <aurele@oules.com>
Co-authored-by: TheCharlatan <seb.kung@gmail.com>

test/functional/rpc_dumptxoutset.py

@@ -43,7 +43,7 @@ class DumptxoutsetTest(BitcoinTestFramework):
         # UTXO snapshot hash should be deterministic based on mocked time.
         assert_equal(
             sha256sum_file(str(expected_path)).hex(),
-            'b1bacb602eacf5fbc9a7c2ef6eeb0d229c04e98bdf0c2ea5929012cd0eae3830')
+            '3263fc0311ea46415b85513a59ad8fe67806b3cdce66147175ecb9da768d4a99')
 
         assert_equal(
             out['txoutset_hash'], 'a0b7baa3bf5ccbd3279728f230d7ca0c44a76e9923fca8f32dbfd08d65ea496a')