remove redundant test case in CharSetUtilsTest#testDelete_StringStringarray (#1540)

Author: IcoreE

src/test/java/org/apache/commons/lang3/CharSetUtilsTest.java

@@ -156,7 +156,6 @@ void testDelete_StringStringarray() {
         assertEquals("ho", CharSetUtils.delete("hello", "el"));
         assertEquals("", CharSetUtils.delete("hello", "elho"));
         assertEquals("hello", CharSetUtils.delete("hello", ""));
-        assertEquals("hello", CharSetUtils.delete("hello", ""));
         assertEquals("", CharSetUtils.delete("hello", "a-z"));
         assertEquals("", CharSetUtils.delete("----", "-"));
         assertEquals("heo", CharSetUtils.delete("hello", "l"));