higher review requirement for adding new APIs

tools/diff_api.py

@@ -20,9 +20,7 @@ for each_diff in result:
     if each_diff[0] in ['-', '?']:  # delete or change API is not allowed
         error = True
     elif each_diff[0] == '+':
-        # only new layers is allowed.
+        error = True
-        if not each_diff.startswith('+ paddle.fluid.layers.'):
-            error = True
 
     if each_diff[0] != ' ':
         print(each_diff)