R1:aea46e55dac0

Fix an issue where "Request Review" of a fully-accepted revision would transition to "Accepted"

Summary:
Ref T10967. This is explained in more detail in T10967#217125

When an author does "Request Review" on an accepted revision, void (in the sense of "cancel out", like a bank check) any "accepted" reviewers on the current diff.

Test Plan:
- Create a revision with author A and reviewer B.
- Accept as B.
- "Request Review" as A.
- (With sticky accepts enabled.)
- Before patch: revision swithced…