move point_utils from mmcv to mmseg

[xvjiarui]

Fixed #126

[codecov]

Codecov Report

Merging #128 into master will decrease coverage by 0.08%.
The diff coverage is 69.56%.

@@            Coverage Diff             @@
##           master     #128      +/-   ##
==========================================
- Coverage   82.20%   82.12%   -0.09%     
==========================================
  Files          84       85       +1     
  Lines        3974     3994      +20     
  Branches      614      616       +2     
==========================================
+ Hits         3267     3280      +13     
- Misses        576      581       +5     
- Partials      131      133       +2     

Flag	Coverage Δ
#unittests	82.12% <69.56%> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
mmseg/ops/point_utils.py	65.00% <65.00%> (ø)
mmseg/models/decode_heads/point_head.py	96.55% <100.00%> (-0.03%)	⬇️
mmseg/ops/__init__.py	100.00% <100.00%> (ø)

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[hellock]

mmcv-full is required, and this PR will be closed.