Flag config removal - screenshot optimizations

Removes ce_fence_promise and single_hop_screenshot from config.
Usages in code otherwise have already been removed.

Bug: b/409610064, b/409611877
Test: atest SurfaceFlinger_test
Flag: EXEMPT, flag removal
Change-Id: I9be2a2628eb929d1e8c12d8f09272d77057b7637