docs: remove log4net

[bmorelli25]

Per https://github.com/elastic/sdh-apm/issues/809, we should remove the Log4Net documentation.

[bmorelli25]

@elasticmachine, run elasticsearch-ci/docs

[apmmachine]

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• Start Time: 2023-01-09T20:25:19.486+0000

• Duration: 16 min 56 sec

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Test	Results
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Passed	154
Skipped	2
Total	156

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