Created by: liym27

Required（必填, multiple choices, two at most）

• PR type（PR 类型） is ( B ): A. New features（新功能）---------------- D. Performance optimization（性能优化） B. Bug fixes（问题修复）------------------ E. Breaking changes（向后不兼容的改变） C. Function optimization（功能优化）------F. Others（其它）

• PR changes（改动点）is ( D ): A. OPs（operators）---------------------- C. Docs（文档） B. APIs（接口）--------------------------- D. Others（其它）

• Use one sentence to describe what this PR does.（简述本次PR的目的和改动）

1. Remove target vars of gast.For from before_loop_vars or after_loop_vars
2. fix bug of condition_vars: condition_vars should only contain vars in current loop node, should not contain the target vars of child loop node or parent loop node.

Optional（选填, If None, please delete it）

• Describe what this PR does in detail. If this PR fixes an issue, please give the issue id.

For example:

for i in range(tensor_a): # condition_vars of this for loop is `i`, not `i and j`
   # for this for loop, variable j should not in after_loop_vars. This PR fix it.      
   for j in range(int_b):   # condition_vars of this for loop is `j`, not `i and j`
       # do something

# for this for loop, variable i should not in before_loop_body_vars. This PR fix it.      
for j in range(tensor_c): 
    # do something

• If you modified docs, please make sure that both Chinese and English docs were modified and provide a preview screenshot. （文档必填）

• Please write down other information you want to tell reviewers.