It is always advisable to take IELTS or TOEFL just to be safe, especially if you are not from a native English speaking country like USA, UK, Canada, Australia or New Zealand. This is because there have been a lot of cases where applicants couldn’t score a 6.0 in IELTS which is the minimum score for most English-taught programs in Germany despite all their previous education being in English.
If your university accepted that all your previous education was in English and waived IELTS or TOEFL, then I think that is enough. The embassy might only require a letter from your university and previous educational institutions stating your education was entirely in English and as such do not require IELTS or TOEFL. However, if during the interview, they realize that your level of English is inferior even though all your previous education was in English, it can lead to your visa being rejected.