Revert "[Executorch] optimized sigmoid"

[swolchok]

This reverts commit 5b4d9bbf4a7d6e23ad2d4a7a575ecc66d588664b. Attempting to debug/fix #7019.

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• [DomainsOnly] Jobs fail with GLIBC version not found

:x: 1 New Failure

As of commit e96b2617778029c5544cadfc910a38f68833297b with merge base 0070680ce04e274aaa4c2082e2fb26335f6f9f13 ():

NEW FAILURE - The following job has failed:

* [Check Labels / Check labels](https://hud.pytorch.org/pr/pytorch/executorch/7020#33348468614) ([gh](https://github.com/pytorch/executorch/actions/runs/11961690399/job/33348468614)) `RuntimeError: Error checking labels: PR does not have required labels`

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