Simplify _get_script_fn in test_ops.py

[NicolasHug]

This PR removes the wrappers used in get_srcipt_gn as they're not needed anymore.

I'm not sure we can completely get rid of get_script_fn, as it doesn't seem possible to script self.fn: NotSupportedError: Compiled functions can't take variable number of arguments or use keyword-only arguments with defaults:.

[codecov]

Codecov Report

Merging #3541 (8cefd56) into master (3428a7d) will decrease coverage by 0.50%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3541      +/-   ##
==========================================
- Coverage   79.26%   78.75%   -0.51%     
==========================================
  Files         105      105              
  Lines        9742     9750       +8     
  Branches     1564     1566       +2     
==========================================
- Hits         7722     7679      -43     
- Misses       1533     1581      +48     
- Partials      487      490       +3     

Impacted Files	Coverage Δ
torchvision/datasets/flickr.py	25.64% <0.00%> (-73.08%)	⬇️
torchvision/models/detection/_utils.py	82.58% <0.00%> (-0.53%)	⬇️
torchvision/transforms/autoaugment.py	94.04% <0.00%> (-0.08%)	⬇️
torchvision/transforms/functional_tensor.py	79.92% <0.00%> (+0.07%)	⬆️
torchvision/__init__.py	63.88% <0.00%> (+2.77%)	⬆️
torchvision/io/video.py	82.06% <0.00%> (+3.26%)	⬆️
torchvision/io/__init__.py	89.65% <0.00%> (+3.44%)	⬆️

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[fmassa]

LGTM, thanks a lot!