input: Write a function to remove all whitespaces from a given string.
  assert remove_whitespace("This is a string with whitespaces") == "Thisisastringwithwhitespaces"
  assert remove_whitespace("   Leading and trailing spaces   ") == "Leadingandtrailingspaces"
  assert remove_whitespace("NoSpacesHere") == "NoSpacesHere"
output: def remove_whitespace(s):
      return s.replace(" ", "")