[rpc] Tidy up reporting of buried and ongoing softforks

This combines reporting of buried (formally ISM) softfork deployments
and BIP9 versionbits softfork deployments into one JSON object in the
getblockchaininfo return object.

test/functional/rpc_blockchain.py

@@ -78,7 +78,6 @@ class BlockchainTest(BitcoinTestFramework):
 
         keys = [
             'bestblockhash',
-            'bip9_softforks',
             'blocks',
             'chain',
             'chainwork',