Revert "zink: always force flushes when originating from api frontend"

This reverts commit 03f049f497.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27560>
(cherry picked from commit 097e543c0a)

.pick_status.json

@@ -1524,7 +1524,7 @@
         "description": "Revert \"zink: always force flushes when originating from api frontend\"",
         "nominated": false,
         "nomination_type": 2,
-        "resolution": 4,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "03f049f49730b8b1268f2975fc34ac2b1f9a4ef9",
         "notes": null

src/gallium/drivers/zink/zink_context.c

@@ -3849,8 +3849,7 @@ zink_flush(struct pipe_context *pctx,
       }
    }
 
-   /* TODO: if swapchains gain timeline semaphore semantics, `flags` can be eliminated and no-op fence can return timeline id */
-   if (!batch->has_work && flags) {
+   if (!batch->has_work) {
        if (pfence) {
           /* reuse last fence */
           fence = ctx->last_fence;