Androidビルドでエラーが直らない

前提

Unity,C#でゲームを作っています。
Unityバージョンは2017.3.1f1です。
サードパーティのプラグインはGitHubとUnityAdsを使っています。
JDKはjdk1.8.0_171です。

問題

Androidビルドでこのエラーが発生しました。直りません。
[Build failure--Unable to convert dasses into dex format.See the Console for details.]

【Unity2018対応】Androidビルドでエラーが出る場合の対処法

これの通りに
1 最新のSDKを入れる
2 toolsフォルダを古い方に交換
3 [Use Highest Installed]を選ぶ
4 Build Systemの項目 [Internal]を選ぶ
5 Other Settings内のScript Backendを『IL2CPP』にする
6 Assets→Reimport Allを実行
7 PC再起動

を試しました。
他に何をすればよいか、ヒントだけでも教えて頂けたら嬉しく思います。

##エラー内容

[Build failure--Unable to convert dasses into dex format.See the Console for details.]

一つ目
OBSOLETE - Providing Android resources in Assets/Plugins/Android/res is deprecated, please move your resources to an AAR or an Android Library. See "AAR plug-ins and Android Libraries" section of the Manual for more details.
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

二つ目
CommandInvokationFailure: Unable to convert classes into dex format.
C:\Java\jdk1.8.0_171\bin\java.exe -Xmx2048M -Dcom.android.sdkmanager.toolsdir="C:/Users/名前/AppData/Local/Android/Sdk\tools" -Dfile.encoding=UTF8 -jar "C:\Program Files\Unity\Editor\Data\PlaybackEngines\AndroidPlayer/Tools\sdktools.jar" -

stderr[
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/BuildConfig;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/IUnityAdsListener;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$1;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$2;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$FinishState;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$PlacementState;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$UnityAdsError;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/adunit/AdUnitActivity;

UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.RuntimeException: Translation has been interrupted
at com.android.dx.command.dexer.Main.processAllFiles(Main.java:608)
at com.android.dx.command.dexer.Main.runMonoDex(Main.java:311)
at com.android.dx.command.dexer.Main.run(Main.java:277)
at com.android.dx.command.dexer.Main.main(Main.java:245)
at com.android.dx.command.Main.main(Main.java:106)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at SDKMain.main(SDKMain.java:130)
Caused by: java.lang.InterruptedException: Too many errors
at com.android.dx.command.dexer.Main.processAllFiles(Main.java:600)
... 9 more
]
stdout[
processing archive C:\Users\名前\Desktop\Unity F\quiz\Temp\StagingArea\android-libraries\UnityAds\libs.\classes.jar...
processing com/unity3d/ads/BuildConfig.class...
processing com/unity3d/ads/IUnityAdsListener.class...
processing com/unity3d/ads/UnityAds.class...
processing com/unity3d/ads/UnityAds$1.class...
processing com/unity3d/ads/UnityAds$2.class...
processing com/unity3d/ads/UnityAds$FinishState.class...
processing com/unity3d/ads/UnityAds$PlacementState.class...
（このprocessing～が続きます）

三つ目
Error building Player: 2 errors

四つ目
Build completed with a result of 'Failed'
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

五つ目
UnityEditor.BuildPlayerWindow+BuildMethodException: 3 errors
at UnityEditor.BuildPlayerWindow+DefaultBuildMethods.BuildPlayer (BuildPlayerOptions options) [0x0020e] in C:\buildslave\unity\build\Editor\Mono\BuildPlayerWindowBuildMethods.cs:181
at UnityEditor.BuildPlayerWindow.CallBuildMethods (Boolean askForBuildLocation, BuildOptions defaultBuildOptions) [0x00065] in C:\buildslave\unity\build\Editor\Mono\BuildPlayerWindowBuildMethods.cs:88
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

##エラーの概要と予想

1.[Build　Settings]の[Build System]を「Internal」から「Gradle」に変えたところ、今まではすぐにエラーが出てきたのですが、ビルドの直前（Building）でエラーが発生するようになりました。

2.一つ目のエラー
OBSOLETE - Providing Android resources in Assets/Plugins/Android/res is deprecated, please move your resources to an AAR or an Android Library. See "AAR plug-ins and Android Libraries" section of the Manual for more details.
ここが問題らしい気がするのですが、どうすれば直るのか分かりません。

3.質問なのですが、このエラーの問題は「Plugins」の中にあるのでしょうか？