test: Avoid empty errmsg in JSONRPCException

It is unclear why the fallback should be an empty message, when it is
better to include all rpc_error details that are available.

Also, include the http status.

This allows to revert commit 6354b4fd7f,
because it is no longer needed.

test/functional/test_framework/authproxy.py

@@ -51,11 +51,7 @@ log = logging.getLogger("BitcoinRPC")
 
 class JSONRPCException(Exception):
     def __init__(self, rpc_error, http_status=None):
-        try:
-            errmsg = '%(message)s (%(code)i)' % rpc_error
-        except (KeyError, TypeError):
-            errmsg = ''
-        super().__init__(errmsg)
+        super().__init__(f"{rpc_error} [http_status={http_status}]")
         self.error = rpc_error
         self.http_status = http_status