input: Write a python function that eliminates segments comprising only lowercase letters from an input string.
  assert remove_lowercase("PYTHon")==('PYTH')
  assert remove_lowercase("FInD")==('FID')
  assert remove_lowercase("STRinG")==('STRG')
output: def remove_lowercase(input_string):
      return ''.join([char for char in input_string if not char.islower()])