input: Write a function to remove all HTML tags from a given string. The function should return the cleaned string without any HTML tags.
  
  def clean_html_tags(str):
      clean_str = re.sub("<.*?>", "", str)
      return clean_str
  
  assert clean_html_tags("<p>This is a <b>test</b> string</p>") == "This is a test string"
  assert clean_html_tags("<div><h1>Title</h1><p>Content here</p></div>") == "TitleContent here"
  assert clean_html_tags("<a href='example.com'>Link</a>") == "Link"
  assert clean_html_tags("<img src='image.jpg' alt='Image'>") == ""
  assert clean_html_tags("No tags here") == "No tags here"
output: def clean_html_tags(str):
      clean_str = re.sub("<.*?>", "", str)
      return clean_str