Avoid processing already processed tick

To avoid overly ticking, we only want to tick when:
1. the last submitted serial has moved beyond the completed serial
2. or the completed serial has not reached the future command serial added
by the trackers (MapRequestTracker, FenceSignalTracker, ErrorScopeTracker).

Bug: dawn:400
Change-Id: Ie7c65acc332846ac1a27f9a18f230149d96d2189
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/19062
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Natasha Lee <natlee@microsoft.com>

src/dawn_native/null/DeviceNull.cpp

@@ -185,8 +185,6 @@ namespace dawn_native { namespace null {
     }
 
     MaybeError Device::WaitForIdleForDestruction() {
-        // Fake all commands being completed
-        AssumeCommandsComplete();
         return {};
     }