Get rid of defvalue for [arg, index]
This was a hidden bug that causes flows w/ non-zero indices to fail.
@@ -2508,7 +2508,7 @@ def schema_arg(cfg):
'lock': 'false',
'require': None,
'signature': None,
- 'defvalue': '0',
+ 'defvalue': None,
'shorthelp': 'Current index',
'example': ["cli: -arg_index 0",
"api: chip.set('arg','index','0')"],
