move warning of ParallelExecutor (#17945)

test=develop

Author: chengduo

python/paddle/fluid/parallel_executor.py

@@ -125,12 +125,6 @@ def __init__(self,
                  num_trainers=1,
                  trainer_id=0,
                  scope=None):
-        sys.stderr.write(
-            'ParallelExecutor is deprecated. '
-            'Please use CompiledProgram and Executor. CompiledProgram '
-            'is a central place for optimization and Executor is the '
-            'unified executor. Example can be found in compiler.py.\n')
-
         if build_strategy is None:
             build_strategy = BuildStrategy()