refactor: Removed unused imports and prevents XML attacks

[fg-mindee]

This PR introduces the following modifications:

• defuses XML attacks
• removed unused imports

Any feedback is welcome!

[codecov]

Codecov Report

Merging #582 (a4f4a45) into main (c52488c) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #582      +/-   ##
==========================================
- Coverage   96.07%   96.05%   -0.03%     
==========================================
  Files         109      109              
  Lines        4233     4233              
==========================================
- Hits         4067     4066       -1     
- Misses        166      167       +1     

Flag	Coverage Δ
unittests	96.05% <100.00%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
doctr/datasets/classification/base.py	93.54% <100.00%> (-0.40%)	⬇️
doctr/datasets/detection.py	96.96% <100.00%> (ø)
doctr/io/elements.py	92.09% <100.00%> (+0.09%)	⬆️
doctr/models/recognition/crnn/pytorch.py	100.00% <100.00%> (ø)
doctr/models/recognition/crnn/tensorflow.py	100.00% <100.00%> (ø)
doctr/models/recognition/sar/tensorflow.py	98.49% <100.00%> (ø)
doctr/utils/visualization.py	92.03% <100.00%> (ø)
...dels/detection/differentiable_binarization/base.py	91.19% <0.00%> (-0.63%)	⬇️

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