Create a function that will remove the letters "a", "b" and "c" from the given string and return the modified version. If the given string does not contain "a", "b", or "c", return null.
removeABC("Tesha is my world") ➞ "Tesh is my world"
removeABC("This might be a bit hard") ➞ "This might e it hrd"
removeABC("hello world!") ➞ null
removeABC("") ➞ nullIf the given string does not contain "a", "b", or "c", return null.