Revert of AcmReceiver: Ask NetEq to delete all decoders at once instead of one by one (patchset #2 id:20001 of https://codereview.webrtc.org/2342313002/ )

Reason for revert:
Seems to have broken Chromium tests.

Original issue's description:
> AcmReceiver: Ask NetEq to delete all decoders at once instead of one by one
>
> It requires a new NetEq method, but it can no longer fail. And we no
> longer need to use AcmReceiver::decoders_, which we're trying to
> eliminate.
>
> BUG=webrtc:5801
>
> Committed: https://crrev.com/f6232b43a176e1717354b671a0a52b887d70de59
> Cr-Commit-Position: refs/heads/master@{#14275}

TBR=ossu@webrtc.org,henrik.lundin@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:5801

Review-Url: https://codereview.webrtc.org/2349973002
Cr-Commit-Position: refs/heads/master@{#14278}

webrtc/modules/audio_coding/neteq/neteq_impl.h

@@ -123,8 +123,6 @@ class NetEqImpl : public webrtc::NetEq {
   // -1 on failure.
   int RemovePayloadType(uint8_t rtp_payload_type) override;
 
-  void RemoveAllPayloadTypes() override;
-
   bool SetMinimumDelay(int delay_ms) override;
 
   bool SetMaximumDelay(int delay_ms) override;