Reland: Drop the 16kHz sample rate restriction on AECM and zero out higher bands

Landed originally here: https://codereview.webrtc.org/1774553002/
Revertede here: https://codereview.webrtc.org/1781893002/

TBR=solenberg@webrtc.org, tina.legrand@webrtc.org

Review URL: https://codereview.webrtc.org/1777093004

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Cr-Mirrored-Commit: 776593b1399a448de3886301e0614921fdd58892