[Improvement][task-plugin] Remove unreasonable log (#8115)

dolphinscheduler-task-plugin/dolphinscheduler-task-api/src/main/java/org/apache/dolphinscheduler/plugin/task/api/AbstractCommandExecutor.java

@@ -314,7 +314,6 @@ public abstract class AbstractCommandExecutor {
         getOutputLogService.submit(() -> {
             try (BufferedReader inReader = new BufferedReader(new InputStreamReader(process.getInputStream()))) {
                 String line;
-                logBuffer.add("welcome to use bigdata scheduling system...");
                 while ((line = inReader.readLine()) != null) {
                     if (line.startsWith("${setValue(")) {
                         varPool.append(line, "${setValue(".length(), line.length() - 2);