Remove no use out_dir

[linshokaku]

Remove the out_dir argument of Writer.__call__ since it does not affect the behavior of the program.

cf.

pytorch-pfn-extras/pytorch_pfn_extras/writing/_writer_base.py

Line 289 in bc94bc1

out_dir = self.out_dir

[emcastillo]

Discussed offline:

1- This PR is non-compat as some users may directly call writer.save in Extensions or related code
2- In order to avoid disruption there are some alternatives

• Keep the original interface but add a deprecation warning
• Make the out_dir parameter optional (None) and use it to override the Writer.out_dir attribute when needed
• Check the writer's design and think on a large scope if things like out_dir makes sense and how can it affect user codes