input: Write a function to remove all HTML tags from a given string using regular expressions. Return the cleaned string with no 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("No tags here")=="No tags here"
  assert clean_html_tags("<a href='example.com'>Link</a>")=="Link"
  assert clean_html_tags("")==""
output: import re
  
  def clean_html_tags(text):
      return re.sub(r'<.*?>', '', text)