Both means the same, you're regreting the actions of some male person, but when you said "No debió haberlo hecho" also means he may do it again.

'No debió haberlo hecho' and 'no debió hacerlo' mean the same. 1 is correct: 'he shouldn't have done it'. 'He did not have to do it' would be 'no debía hacerlo'. By the way, both sentences could be said about a female or about a male: it's third person singular; apart from that, we don't know anything about the subject.