[FLINK-8148][yarn/s3] fix test instability in YarnFileStageTestS3ITCase

Remove a check for a deleted directory since we may not see our own delete yet
with S3.

This closes #5066.

flink-yarn/src/test/java/org/apache/flink/yarn/YarnFileStageTest.java

@@ -139,7 +139,7 @@ public class YarnFileStageTest extends TestLogger {
 	 * @param addSchemeToLocalPath
 	 * 		whether add the <tt>file://</tt> scheme to the local path to copy from
 	 */
-	public static void testCopyFromLocalRecursive(
+	static void testCopyFromLocalRecursive(
 			FileSystem targetFileSystem,
 			Path targetDir,
 			TemporaryFolder tempFolder,

flink-yarn/src/test/java/org/apache/flink/yarn/YarnFileStageTestS3ITCase.java

@@ -42,7 +42,6 @@ import java.util.Map;
 import java.util.UUID;
 
 import static org.hamcrest.Matchers.greaterThan;
-import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assume.assumeFalse;
 import static org.junit.Assume.assumeNoException;
@@ -166,9 +165,6 @@ public class YarnFileStageTestS3ITCase extends TestLogger {
 
 			YarnFileStageTest.testCopyFromLocalRecursive(fs.getHadoopFileSystem(),
 				new org.apache.hadoop.fs.Path(directory.toUri()), tempFolder, true);
-
-			// now directory must be gone
-			assertFalse(fs.exists(directory));
 		} finally {
 			// clean up
 			fs.delete(basePath, true);