Revert "Moving iOS Audio Device to sdk."

This reverts commit a167212657f8450296ac518162ef0b28ba4214c5.

Reason for revert: Breaks Chromium build.
Log:
https://ci.chromium.org/buildbot/chromium.webrtc.fyi/ios-device/
Writing """\
additional_target_cpus = [ "arm64" ]
goma_dir = "/b/c/goma_client"
ios_enable_code_signing = false
is_component_build = false
is_debug = false
target_cpu = "arm"
target_os = "ios"
use_goma = true
""" to /b/c/b/ios_device/src/out/Release-iphoneos/args.gn.
/b/c/b/ios_device/src/buildtools/mac/gn gen //out/Release-iphoneos --check
  -> returned 1
ERROR at //third_party/webrtc/sdk/BUILD.gn:108:9: Can't load input file.
        "../../rtc_base:checks",
        ^----------------------
Unable to load:
  /b/c/b/ios_device/src/third_party/rtc_base/BUILD.gn
I also checked in the secondary tree for:
  /b/c/b/ios_device/src/build/secondary/third_party/rtc_base/BUILD.gn

Original change's description:
> Moving iOS Audio Device to sdk.
> 
> This change forks the existing iOS audio device module and audio device
> from modules/audio_device/ into sdk/objc/Framework. It also updates
> RTCPeerConnectionFactory to use the forked implementation.
> 
> The unit tests are re-implemented as XCTests.
> 
> Bug: webrtc:9120
> Change-Id: Ie60cafae796efbd7966d21ff6877c92cbe850fb7
> Reviewed-on: https://webrtc-review.googlesource.com/67300
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#23163}

TBR=andersc@webrtc.org,kthelgason@webrtc.org,peterhanspers@webrtc.org

Change-Id: Iebe52e9775409a3bdd6d5e44f4f985d56b859cbe
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9120
Reviewed-on: https://webrtc-review.googlesource.com/75220
Reviewed-by: Max Morin <maxmorin@webrtc.org>
Commit-Queue: Max Morin <maxmorin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23166}

sdk/objc/Framework/Classes/PeerConnection/RTCPeerConnectionFactory.mm

@@ -38,10 +38,6 @@
 #include "sdk/objc/Framework/Native/src/objc_video_encoder_factory.h"
 #endif
 
-#if defined(WEBRTC_IOS)
-#import "sdk/objc/Framework/Native/api/audio_device_module.h"
-#endif
-
 // Adding the nogncheck to disable the including header check.
 // The no-media version PeerConnectionFactory doesn't depend on media related
 // C++ target.
@@ -59,14 +55,6 @@
 
 @synthesize nativeFactory = _nativeFactory;
 
-- (rtc::scoped_refptr<webrtc::AudioDeviceModule>)audioDeviceModule {
-#if defined(WEBRTC_IOS)
-  return webrtc::CreateAudioDeviceModule();
-#else
-  return nullptr;
-#endif
-}
-
 - (instancetype)init {
 #ifdef HAVE_NO_MEDIA
   return [self initWithNoMedia];
@@ -77,7 +65,7 @@
                                                      [[RTCVideoEncoderFactoryH264 alloc] init])
                        nativeVideoDecoderFactory:webrtc::ObjCToNativeVideoDecoderFactory(
                                                      [[RTCVideoDecoderFactoryH264 alloc] init])
-                               audioDeviceModule:[self audioDeviceModule]
+                               audioDeviceModule:nullptr
                            audioProcessingModule:nullptr];
 #endif
 }
@@ -99,7 +87,7 @@
                        nativeAudioDecoderFactory:webrtc::CreateBuiltinAudioDecoderFactory()
                        nativeVideoEncoderFactory:std::move(native_encoder_factory)
                        nativeVideoDecoderFactory:std::move(native_decoder_factory)
-                               audioDeviceModule:[self audioDeviceModule]
+                               audioDeviceModule:nullptr
                            audioProcessingModule:nullptr];
 #endif
 }