[AIRFLOW-4192] Remove tables from the task context variables

[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-4192
  • 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

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After #5010 ending up in an endless discussion, nobody has commented on tables in the task context. It was added with one of the very first commits of the project (dc9537d), I don't know of any users plus it's untested and undocumented, so I suggest we remove it.

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":
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  4. Subject uses the imperative mood ("add", not "adding")
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  6. Body explains "what" and "why", not "how"

Documentation

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Code Quality

• Passes flake8

[Fokko]

LGTM