Inconsistency between configuration and code in the Missed objective of object detection

[mzweilin]

MART/mart/configs/attack/objective/object_detection_missed.yaml

Lines 5 to 7 in 6184ca7

	arg_keys:
	- preds
	kwarg_keys: null

MART/mart/attack/objective/object_detection.py

Line 68 in 6184ca7

def __call__(self, preds, target):

The code requires preds and target, but the configuration only gives preds. Since target is not used in the objective function, we can either delete it from __call__()'s argument list, or add an unused parameter target in the configuration.

[dxoigmn]

This is partially related to #178. We should probably just remove the use of CallWith here. It was meant to be an internal class anyway.