Remove an unused method in novaclient/shell.py

The 'positive_non_zero_float' method has not been used
since Ifc9ddc08614e28358229db84cb9b54552ca36d51.

TrivialFix
Change-Id: Ice0c8f15dbc1a027710e0ace6c8fa872b964c3b6

novaclient/shell.py

@@ -211,20 +211,6 @@ class DeprecatedAction(argparse.Action):
             action(parser, namespace, values, option_string)
 
 
-def positive_non_zero_float(text):
-    if text is None:
-        return None
-    try:
-        value = float(text)
-    except ValueError:
-        msg = _("%s must be a float") % text
-        raise argparse.ArgumentTypeError(msg)
-    if value <= 0:
-        msg = _("%s must be greater than 0") % text
-        raise argparse.ArgumentTypeError(msg)
-    return value
-
-
 class SecretsHelper(object):
     def __init__(self, args, client):
         self.args = args