fix(core): drop the redundant max on the re-read fence value

The re-read is taken from the same fence, later on the same thread, so
under the monotonicity this fix already relies on it can never be below
`current_finished_submission`. The `max` was therefore dead — and in the
one case where it would not be, a backend whose fence regressed, it would
hide that from the assert rather than let it fire.

Author: AdrianEddy

wgpu-core/src/device/resource.rs

@@ -1085,7 +1085,7 @@ impl Device {
                 // high, and the fence is monotonic.
                 let finished_submission =
                     match unsafe { self.raw().get_fence_value(self.fence.as_ref()) } {
-                        Ok(fence_value) => fence_value.max(current_finished_submission),
+                        Ok(fence_value) => fence_value,
                         Err(e) => {
                             let hal_error: WaitIdleError = self.handle_hal_error(e).into();
                             return (user_closures, Err(hal_error));