Simplify comparison in rpc_blockchain.py.

The test for gettxoutsetinfo in rpc_blockchain.py verifies that the
result is the same as before after invalidating and reconsidering a
block.  The comparison has to exclude the 'disk_size' field, though, as
it is not deterministic.

Instead of comparing all the other fields for equality, this change
explicitly removes the 'disk_size' field and then compares the full
objects.  This makes the intent more explicit (compare everything except
for disk_size, not compare just a given list of fields) and also the
code simpler.

test/functional/rpc_blockchain.py

@@ -194,13 +194,10 @@ class BlockchainTest(BitcoinTestFramework):
         node.reconsiderblock(b1hash)
 
         res3 = node.gettxoutsetinfo()
-        assert_equal(res['total_amount'], res3['total_amount'])
-        assert_equal(res['transactions'], res3['transactions'])
-        assert_equal(res['height'], res3['height'])
-        assert_equal(res['txouts'], res3['txouts'])
-        assert_equal(res['bogosize'], res3['bogosize'])
-        assert_equal(res['bestblock'], res3['bestblock'])
-        assert_equal(res['hash_serialized_2'], res3['hash_serialized_2'])
+        # The field 'disk_size' is non-deterministic and can thus not be
+        # compared between res and res3.  Everything else should be the same.
+        del res['disk_size'], res3['disk_size']
+        assert_equal(res, res3)
 
     def _test_getblockheader(self):
         node = self.nodes[0]