Anywone who can view quiz reports can delete student attempts

Giving someone permission to view quiz reports probably implies a lower level of trust than giving the ability to delete student's work. However, at the moment they are controlled by the same capability.

Hmm. Actually there is a 'Delete quiz attempts' capability. It is just not being used anywhere.

Similarly, I will limit the regrade functionality to people with 'Grade quizzes manually' capability.