So these verses are not in the Quran?:

Sura 4:89:

"They wish that you should reject faith as they reject faith, and then you would be equal; therefore take not to yourselves friends of them, until they emigrate in the way of God; then, if they turn their backs, take them, and slay them wherever you find them; take not to yourselves any one of them as friend or helper."

I don't think that could be interpreted any other way than that apostates should be killed.