fix decoding error when clip grad op and python==2 (#33937)

tools/remove_grad_op_and_kernel.py

@@ -20,6 +20,7 @@ import os
 import sys
 import re
 import glob
+import io
 
 
 def find_type_files(cur_dir, file_type, file_list=[]):
@@ -124,7 +125,7 @@ if __name__ == '__main__':
             custom_pattern2 = custom_pattern2[:-1]
 
         all_matches = []
-        with open(op_file, 'r', encoding='utf-8') as f:
+        with io.open(op_file, 'r', encoding='utf-8') as f:
             content = ''.join(f.readlines())
 
             op, op_count = remove_grad_op_and_kernel(content, op_pattern1,
@@ -157,8 +158,8 @@ if __name__ == '__main__':
         for i in all_matches:
             content = content.replace(i, '')
 
-        with open(op_file, 'w') as f:
-            f.write(content)
+        with io.open(op_file, 'w', encoding='utf-8') as f:
+            f.write(u'{}'.format(content))
 
     # 2. update operators/CMakeLists.txt
     cmake_file = os.path.join(tool_dir,