[AIRFLOW-4206] Python 2 removal - remove explicit inheritance of object

[BasPH]

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Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-4206
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.
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Description

• Here are some details about my PR, including screenshots of any UI changes:

Python 3 classes implicitly inherit from object so there's no need anymore to define class MyClass(object): ... (in Python 3 this is equivalent to class MyClass: ...). In this PR I removed all such cases.

Note that https://jira.apache.org/jira/browse/AIRFLOW-4197 must be merged before this PR, since (obviously) the Python 2 jobs are failing.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

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  • All the public functions and the classes in the PR contain docstrings that explain what it does
  • If you implement backwards incompatible changes, please leave a note in the Updating.md so we can assign it to a appropriate release

Code Quality

• Passes flake8

[Fokko]

Can you rebase onto master?

[codecov-io]

Codecov Report

Merging #5021 into master will decrease coverage by <.01%.
The diff coverage is 92.1%.

@@            Coverage Diff             @@
##           master    #5021      +/-   ##
==========================================
- Coverage   78.68%   78.67%   -0.01%     
==========================================
  Files         470      470              
  Lines       30018    30013       -5     
==========================================
- Hits        23619    23614       -5     
  Misses       6399     6399

Impacted Files	Coverage Δ
...ow/contrib/auth/backends/github_enterprise_auth.py	0% <0%> (ø)	⬆️
airflow/contrib/auth/backends/google_auth.py	0% <0%> (ø)	⬆️
...rflow/contrib/utils/mlengine_prediction_summary.py	0% <0%> (ø)	⬆️
airflow/www/utils.py	82.7% <100%> (ø)	⬆️
airflow/bin/cli.py	66.83% <100%> (ø)	⬆️
airflow/utils/state.py	96.29% <100%> (-0.14%)	⬇️
airflow/dag/base_dag.py	66.66% <100%> (ø)	⬆️
airflow/contrib/hooks/bigquery_hook.py	61.08% <100%> (ø)	⬆️
airflow/executors/celery_executor.py	76.92% <100%> (ø)	⬆️
airflow/executors/local_executor.py	82.35% <100%> (ø)	⬆️
... and 23 more

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[BasPH]

@Fokko rebased