clear_null_account_balance deprecated

Author: inertia186

_data/apidefinitions/broadcast_ops.yml

@@ -1395,8 +1395,13 @@
     - name: clear_null_account_balance
       since: HF20
       virtual: true
+      deprecated: true
       purpose: |
-         For per-block processing that clears null account balances. See: [#2627](https://github.com/steemit/steem/issues/2627)
+         Deprecated as of HF23, see: [#3556](https://github.com/steemit/steem/issues/3556).
+         
+         For per-block processing that clears null account balances (prior to HF23).
+         
+         See: [#2627](https://github.com/steemit/steem/issues/2627)
       roles:
         - active
           owner