Revert "Add testing hints (flutter#39868)" (flutter#39921)

Revert "Add testing hints"

Author: zanderso

testing/README.md

@@ -947,12 +947,7 @@ def run_engine_tasks_in_parallel(tasks):
 
 
 def main():
-  parser = argparse.ArgumentParser(
-      description='''
-In order to learn the details of running tests in the engine, please consult the
-Flutter Wiki page on the subject: https://github.com/flutter/flutter/wiki/Testing-the-engine
-'''
-  )
+  parser = argparse.ArgumentParser()
   all_types = [
       'engine', 'dart', 'benchmarks', 'java', 'android', 'objc', 'font-subset'
   ]