Revert "RNN VAD: Replace Ooura with PFFFT for the pitch auto correlation."

This reverts commit 8fcd6537f242ffd74154a62dad410e573e2efc4b.

Reason for revert: broke internal projects.

Original change's description:
> RNN VAD: Replace Ooura with PFFFT for the pitch auto correlation.
> 
> Bug: webrtc:9577, webrtc:10480
> Change-Id: I6d58866d48b8eaaa4102551b88d4f55133d1915c
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130482
> Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
> Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#27387}

TBR=gustaf@webrtc.org,alessiob@webrtc.org

Change-Id: Ia05057326ebc277f334b13db0bfec9d4442903c2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9577, webrtc:10480
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130369
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Commit-Queue: Qingsi Wang <qingsi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27405}