Fix Fragment tests after androidx stubs update

Author: atorralba

java/ql/test/library-tests/frameworks/android/sources/TestActivityAndFragment.java

@@ -1,7 +1,7 @@
 import android.app.Activity;
-import android.app.Fragment;
 import android.content.Intent;
 import android.os.Bundle;
+import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentTransaction;
 
 public class TestActivityAndFragment extends Activity {

java/ql/test/query-tests/security/CWE-470/MainActivity.java

@@ -1,11 +1,7 @@
 package com.example.myapp;
 
-import android.app.Fragment;
 import android.os.Bundle;
-import android.view.LayoutInflater;
-import android.view.View;
-import android.view.ViewGroup;
-import android.widget.Button;
+import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentActivity;
 import androidx.fragment.app.FragmentTransaction;