This is not quite correct. You cannot actually remove the question from the quiz after it has been taken by the class...
But you can give zero marks for the question and have it re-marked out of the new lower total score, which achieves the same thing as far as Gradebook is concerned.
The way to do it is to start by going to the 'cover page' for the quiz and lowering the points assigned to the whole quiz by 1 (say from 10 to 9). It will tell you that you need to regrade (which we will in a minute). Click on Save at the bottom of the page.
The obvious next step would be to go into the quiz - don't do that. Instead go into Speedgrader. Click on Regrade for the bad question. Set the points to zero and hit Regrade. It will ask how you want to apply it - leave it on the default and click Regrade.
The question should now be worth zero, and the overall quiz will be out of 9. Everyone's marks should be as if the question was not included in the test.
I feel like this is an ugly hack, but it works.
Note that the actual quiz is unaltered - if you give it again, the bad question will still be there and score 1 point, but the quiz will be out of 9 instead of 10 (not what you want!). So make sure to go back and edit your quiz for next time.
Also note that you have to do that step of lowering the total quiz score first before trying the regrade. Or bad things happen 🙂