Remove double stop() test in StopWatchTest

StopWatchTest#testBadStates has the same block of code testing
StopWatch#stop copy-pasted.
This patch cleans it up by removing one of those blocks.

src/test/java/org/apache/commons/lang3/time/StopWatchTest.java

@@ -174,13 +174,6 @@ public class StopWatchTest {
             // expected
         }
 
-        try {
-            watch.stop();
-            fail("Calling stop on an unstarted StopWatch should throw an exception. ");
-        } catch (final IllegalStateException ise) {
-            // expected
-        }
-
         try {
             watch.suspend();
             fail("Calling suspend on an unstarted StopWatch should throw an exception. ");