style(StandardJmeterEngine): remove unnecessary code

delete "return" in a private void method

Author: linvaux

src/core/src/main/java/org/apache/jmeter/engine/StandardJMeterEngine.java

@@ -579,7 +579,6 @@ private void startThreadGroup(AbstractThreadGroup group, int groupCount, SearchB
         } catch (JMeterStopTestException ex) { // NOSONAR Reported by log
             JMeterUtils.reportErrorToUser("Error occurred starting thread group :" + group.getName()+ ", error message:"+ex.getMessage()
                 +", \r\nsee log file for more details", ex);
-            return; // no point continuing
         }
     }