The revelations that are abrogated are those revelations that were revealed before the Qur’an, for example the Torah, the Zaboor and the Injeel.
Here Allah (swt) says that He does not cause the previous revelations to be forgotten but He substitutes them with something better or similar, indicating that the Torah, the Zaboor and the Injeel were substituted by the Qur’an.
If we consider that the Arabic word ayat in the above verse refers to the verses of the Qur’an, and not previous revelations, then it indicates that none of the verses of the Qur’an are abrogated by Allah but substituted with something better or similar. This means that certain verses of the Qur’an, that were revealed earlier were substituted by verses that were revealed later. I agree with both the interpretations.
In the English language, the Queen of England refers to herself as ‘We’ instead of ‘I’. This is known as the ‘royal plural’.
Rajiv Gandhi, the ex-Prime Minister of India used to say in Hindi "Hum dekhna chahte hain". "We want to see." ‘Hum’ means ‘We’ which is again a royal plural in Hindi.
Similarly in Arabic, when Allah refers to Himself in the Qur’an, He often uses Arabic word 'Nahnu' meaning ‘We’. It does not indicate plural of number but plural of respect.