input: Write a function to remove all HTML tags from a given string. The function should return the cleaned string without any HTML tags. If the input string is empty, the function should return 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("This is <i>bold</i> text") == "This is bold text"
  assert clean_html_tags("<a href='http://example.com'>Link</a>") == "Link"
  assert clean_html_tags("") == ""
  assert clean_html_tags("No tags here") == "No tags here"
output: def clean_html_tags(s):
      import re
      return re.sub(r'<[^>]+>', '', s)