[Enhancement] Remove unnecessary custom_import from test.py

[Harold-lkk]

#603

[codecov]

Codecov Report

Merging #758 (e3aae2a) into main (e0ff118) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head e3aae2a differs from pull request most recent head 9f65ae7. Consider uploading reports for the commit 9f65ae7 to get more accurate results

@@            Coverage Diff             @@
##             main     #758      +/-   ##
==========================================
- Coverage   84.60%   84.59%   -0.01%     
==========================================
  Files         165      164       -1     
  Lines       10668    10642      -26     
  Branches     1623     1618       -5     
==========================================
- Hits         9026     9003      -23     
+ Misses       1297     1295       -2     
+ Partials      345      344       -1     

Flag	Coverage Δ
unittests	84.59% <ø> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
mmocr/apis/train.py	17.91% <0.00%> (-1.81%)	⬇️
mmocr/utils/setup_env.py

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[gaotongxiao]

Need to resolve the conflict