remove redundent pserver block

Author: typhoonzero

python/paddle/fluid/distribute_transpiler.py

@@ -420,13 +420,14 @@ def __append_optimize_op__(op, block):
 
         # append op to the current block
         per_opt_block = append_block
-        for _, opt_op in enumerate(opt_op_on_pserver):
+        for idx, opt_op in enumerate(opt_op_on_pserver):
             for _, op in enumerate(self.optimize_ops):
                 # optimizer is connected to itself
                 if ufind.is_connected(op, opt_op) and \
                     op not in global_ops:
                     __append_optimize_op__(op, per_opt_block)
-            per_opt_block = pserver_program.create_block(append_block.idx)
+            if idx == len(opt_op_on_pserver) - 1 and global_ops:
+                per_opt_block = pserver_program.create_block(append_block.idx)
 
         # append global ops
         for glb_op in global_ops: