[Refactor] Remove some outdated lines

[zhouzaida]

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Motivation

Due to our lowest supported PyTorch is 1.3.0, I remove the condition to check whether PyTorch version is lower than 1.0 in get_dist_info()

Modification

modify get_dist_info()

BC-breaking (Optional)

No

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects, like MMDet or MMCls.
• CLA has been signed and all committers have signed the CLA in this PR.

[Junjun2016]

Please fix the CI error!

[codecov]

Codecov Report

Merging #1370 (d50ea24) into master (a90b397) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1370      +/-   ##
==========================================
+ Coverage   68.57%   68.59%   +0.01%     
==========================================
  Files         164      164              
  Lines       10897    10891       -6     
  Branches     1993     1991       -2     
==========================================
- Hits         7473     7471       -2     
+ Misses       3032     3030       -2     
+ Partials      392      390       -2     

Flag	Coverage Δ
unittests	68.59% <0.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
mmcv/runner/dist_utils.py	51.06% <0.00%> (+1.06%)	⬆️

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