rpc: Argument name consistency

The meaning is clear from the context, and we're inconsistent here.
Also save typing when using named arguments.

- `bitcoinaddress` -> `address`
- `bitcoinprivkey` -> `privkey`
- `bitcoinpubkey` -> `pubkey`

src/rpc/blockchain.cpp

@@ -875,7 +875,7 @@ UniValue gettxout(const JSONRPCRequest& request)
             "     \"reqSigs\" : n,          (numeric) Number of required signatures\n"
             "     \"type\" : \"pubkeyhash\", (string) The type, eg pubkeyhash\n"
             "     \"addresses\" : [          (array of string) array of bitcoin addresses\n"
-            "        \"bitcoinaddress\"     (string) bitcoin address\n"
+            "        \"address\"     (string) bitcoin address\n"
             "        ,...\n"
             "     ]\n"
             "  },\n"