Fix deprecated warning

app/src/main/java/com/hippo/ehviewer/Settings.java

@@ -19,8 +19,6 @@ package com.hippo.ehviewer;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.net.Uri;
-import android.os.Build;
-import android.preference.PreferenceManager;
 import android.util.Log;
 import android.view.Display;
 import android.view.WindowManager;
@@ -28,6 +26,7 @@ import android.view.WindowManager;
 import androidx.annotation.DimenRes;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.preference.PreferenceManager;
 
 import com.hippo.ehviewer.client.EhConfig;
 import com.hippo.ehviewer.client.EhUtils;