Use Guava's `MoreFiles` for recursive deletion.

The Apache `FileUtils.deleteDirectory` has historically been unstable.
Most recently,
https://issues.apache.org/jira/projects/IO/issues/IO-862
causes `SymlinkValidatorTest` to fail at HEAD.

Change-Id: Id783a2b9fdd67608d72bdd3b6fbf03ccd4cbe425
diff --git a/src/test/java/com/googlesource/gerrit/plugins/uploadvalidator/ValidatorTestCase.java b/src/test/java/com/googlesource/gerrit/plugins/uploadvalidator/ValidatorTestCase.java
index 07a78ab..2702f95 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/uploadvalidator/ValidatorTestCase.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/uploadvalidator/ValidatorTestCase.java
@@ -14,9 +14,9 @@
 
 package com.googlesource.gerrit.plugins.uploadvalidator;
 
+import com.google.common.io.MoreFiles;
 import java.io.File;
 import java.io.IOException;
-import org.apache.commons.io.FileUtils;
 import org.eclipse.jgit.lib.Repository;
 import org.junit.After;
 import org.junit.Before;
@@ -36,7 +36,7 @@
   public void cleanup() throws IOException {
     repo.close();
     if (repoFolder.exists()) {
-      FileUtils.deleteDirectory(repoFolder);
+      MoreFiles.deleteRecursively(repoFolder.toPath());
     }
   }
 }