Revert "Deprecate the adaptive level controller"

This reverts commit 6f37ed78d99daa36e964ff0a65b205f0916d9949.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Deprecate the adaptive level controller
> 
> Level control handled by default-on AGC.
> 
> Bug: none
> Change-Id: I405daeceece12c896d41156b649fcfd556726f77
> Reviewed-on: https://webrtc-review.googlesource.com/59682
> Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
> Reviewed-by: Alex Loiko <aleloi@webrtc.org>
> Commit-Queue: Sam Zackrisson <saza@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22305}

TBR=solenberg@webrtc.org,saza@webrtc.org,aleloi@webrtc.org

Change-Id: Ic52f41fcbebfd2291a51b17ac788313e1ceef163
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: none
Reviewed-on: https://webrtc-review.googlesource.com/60240
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22308}
diff --git a/modules/audio_processing/include/config.h b/modules/audio_processing/include/config.h
index 7615f62..7c34de8 100644
--- a/modules/audio_processing/include/config.h
+++ b/modules/audio_processing/include/config.h
@@ -35,7 +35,7 @@
   kIntelligibility,
   kEchoCanceller3,  // Deprecated
   kAecRefinedAdaptiveFilter,
-  kLevelControl  // Deprecated
+  kLevelControl
 };
 
 // Class Config is designed to ease passing a set of options across webrtc code.