Remove outdated PySpark experimental warning in example

[andrejpk]

Purpose of this PR

Confusing warning in the Python example that Python support is experimental. Python support seems stable in current versions, correct?

Proposed changes: Remove outdated (?) warning in the pyspark example that Python support is experimental. (This was written 6 years ago)

Change Category

Indicate the type of change by marking the applicable boxes:

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] Feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that could affect existing functionality)
• [x] Documentation update

Rationale

This is confusing if no longer correct.

Checklist

Before submitting your PR, please review the following:

• [x] I have conducted a self-review of my own code.
• [x] I have updated documentation accordingly.
• [x] I have added tests that prove my changes are effective or that my feature works.
• [x] Existing unit tests pass locally with my changes.

Additional Notes

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vara-bonthu

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• ~~OWNERS~~ [vara-bonthu]

Approvers can indicate their approval by writing /approve in a comment Approvers can cancel approval by writing /approve cancel in a comment