input: Write a function to remove HTML tags from a given string. The function should use regular expressions to replace any HTML tags with an empty string.
  assert clean_html_tags("<p>This is a <b>test</b> string</p>")=="This is a test string"
  assert clean_html_tags("<div><a href='#'>Link</a></div>")=="Link"
  assert clean_html_tags("<h1>Header</h1>")=="Header"
  assert clean_html_tags("No tags here")=="No tags here"
  assert clean_html_tags("")==""
output: import re
  
  def clean_html_tags(text):
      return re.sub(r'<[^>]+>', '', text)