[Enhancement] Simplify EditLogProcessor and corresponding unit test

[LeoXing1996]

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Motivation

MMEngine support _get_dataloader_size in open-mmlab/mmengine#972. Therefore we can simplify the logic of EditLogProcessor.

Modification

Overwrite _get_dataloader_size and remove duplicate codes with MMEngine.

Who can help? @ them here!

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

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.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (a175a41) 88.14% compared to head (77a51be) 88.16%.

❗ Current head 77a51be differs from pull request most recent head 60f5f30. Consider uploading reports for the commit 60f5f30 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #1694      +/-   ##
===========================================
+ Coverage    88.14%   88.16%   +0.01%     
===========================================
  Files          399      399              
  Lines        26414    26348      -66     
  Branches      4124     4108      -16     
===========================================
- Hits         23282    23229      -53     
+ Misses        2245     2238       -7     
+ Partials       887      881       -6     

Flag	Coverage Δ
unittests	88.16% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
mmedit/engine/runner/log_processor.py	100.00% <100.00%> (+17.56%)	⬆️

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[zengyh1900]

lgtm