Remove redundant self.init_cfg

[jshilong]

Motivation

Actually init_cfg would be set in BaseModule, self.init_cg in subclass is redundant．

##BC-breaking
None

[codecov]

Codecov Report

Merging #959 (5a5fe69) into master (ae41150) will increase coverage by 0.02%.
The diff coverage is n/a.

❗ Current head 5a5fe69 differs from pull request most recent head 46c4e05. Consider uploading reports for the commit 46c4e05 to get more accurate results

@@            Coverage Diff             @@
##           master     #959      +/-   ##
==========================================
+ Coverage   65.64%   65.66%   +0.02%     
==========================================
  Files         149      149              
  Lines        9455     9452       -3     
  Branches     1722     1722              
==========================================
  Hits         6207     6207              
+ Misses       2928     2925       -3     
  Partials      320      320              

Flag	Coverage Δ
unittests	65.66% <ø> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
mmcv/cnn/bricks/transformer.py	0.00% <ø> (ø)

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