input: Write a function to clean a string of HTML tags by removing all HTML tags from the given string. The function should return the cleaned string without any HTML tags.
  assert clean_html_tags("<p>This is a <b>test</b> string</p>")=="This is a test string"
  assert clean_html_tags("<div><h1>Heading</h1><p>Paragraph</p></div>")=="HeadingParagraph"
  assert clean_html_tags("<span>Simple text</span>")=="Simple text"
  assert clean_html_tags("<a href='example.com'>Link</a>")=="Link"
  assert clean_html_tags("<img src='image.jpg'>")==""
output: def clean_html_tags(text):
      import re
      return re.sub(r'<.*?>', '', text)