chore: Revapi now deletes its own comments before commenting

[surli]

Fix #1426

[monperrus]

What about something slightly more powerful?

#spoon-bot posts only if the computed API changes are different from the last post.
last_post = None
for comment in pr.get_comments():
  if comment.user == gh.get_user():
                last_post = comment
if comment.text != file_content:
  comment.delete()
  pr.create_issue_comment(file_content)

[surli]

I prefer the idea which consist in always deleting older comments from revapi, as it will also avoid duplicate message with a different order in changes and it ensures that we always have the very last report message from revapi.

[monperrus]

ok, let's try this and see how it feels. Thanks.