[Fix] complete training hooks.

[bladrome]

Motivation

There is no reason to ignore custom_hooks.

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 tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

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

[codecov]

Codecov Report

Merging #1236 (a9a120c) into master (cd067a9) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master    #1236   +/-   ##
=======================================
  Coverage   83.44%   83.44%           
=======================================
  Files         205      205           
  Lines       16625    16625           
  Branches     2976     2976           
=======================================
  Hits        13872    13872           
  Misses       2001     2001           
  Partials      752      752           

Flag	Coverage Δ
unittests	83.36% <0.00%> (ø)

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

Impacted Files	Coverage Δ
mmpose/apis/train.py	22.53% <0.00%> (ø)

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[ly015]

@bladrome Thank you very much for your help!

I made a minor modification to this PR to not expose timer_config, suggested by mmcv authors.