Delete unused methods.

app/src/main/java/chat/rocket/android/helper/OkHttpHelper.java

 package chat.rocket.android.helper;
 
 import android.content.Context;
-import android.support.annotation.NonNull;
 import com.facebook.stetho.okhttp3.StethoInterceptor;
 
-import java.io.IOException;
 import java.util.concurrent.TimeUnit;
 import chat.rocket.android.RocketChatCache;
 import chat.rocket.android.api.rest.CookieInterceptor;
 import chat.rocket.android.api.rest.DefaultCookieProvider;
-import okhttp3.Call;
-import okhttp3.Callback;
 import okhttp3.OkHttpClient;
-import okhttp3.Request;
-import okhttp3.Response;
 
 /**
  * Helper class for OkHttp client.
  */
 public class OkHttpHelper {
-  private static OkHttpClient defaultHttpClient;
   private static OkHttpClient httpClientForUploadFile;
   private static OkHttpClient httpClientForDownloadFile;
   private static OkHttpClient httpClientForWS;
-  private static String contentType;
-
-  public static OkHttpClient getDefaultHttpClient() {
-    if (defaultHttpClient == null) {
-      defaultHttpClient = new OkHttpClient();
-    }
-    return defaultHttpClient;
-  }
 
   public static OkHttpClient getClientForDownloadFile(Context context) {
     if (httpClientForDownloadFile == null) {
@@ -63,28 +48,4 @@ public class OkHttpHelper {
     }
     return httpClientForWS;
   }
-
-  public static String getContentType(String uri) {
-    Request request = new Request.Builder()
-        .url(uri)
-        .head()
-        .build();
-    getDefaultHttpClient().newCall(request).enqueue(new Callback() {
-      @Override
-      public void onFailure(@NonNull Call call, @NonNull IOException ioException) {
-        ioException.printStackTrace();
-      }
-
-      @Override
-      public void onResponse(@NonNull Call call, @NonNull final Response response)
-          throws IOException {
-        if (!response.isSuccessful()) {
-          throw new IOException("Unexpected code: " + response);
-        } else {
-          contentType = response.header("Content-Type");
-        }
-      }
-    });
-    return contentType;
-  }
 }
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