input: Write a python function to remove all whitespaces from a string.
  assert remove_whitespaces("Hello World") == "HelloWorld"
  assert remove_whitespaces("   Leading and trailing spaces   ") == "Leadingandtrailingspaces"
  assert remove_whitespaces("Multiple   spaces   between") == "Multiplespacesbetween"
  assert remove_whitespaces("NoSpaces") == "NoSpaces"
output: def remove_whitespaces(s):
      return s.replace(" ", "")