scx_rustland: avoid using SCX_ENQ_PREEMPT

With the introduction of a the dynamic time slice that scales down based
on the number of tasks in the system, there is no obvious benefit in
utilizing SCX_ENQ_PREEMPT to dispatch the user-space scheduler.

The reduced time slice as the task count increases already enhances the
user-space scheduler's opportunities to run and efficiently manage
scheduling tasks, even when the system is massively overloaded.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

scheds/rust/scx_rustland/src/bpf/main.bpf.c

@@ -461,7 +461,7 @@ static void dispatch_user_scheduler(s32 cpu)
 		scx_bpf_error("Failed to find usersched task %d", usersched_pid);
 		return;
 	}
-	dispatch_task(p, cpu, SCX_ENQ_PREEMPT);
+	dispatch_task(p, cpu, 0);
 	__sync_fetch_and_add(&nr_kernel_dispatches, 1);
 	bpf_task_release(p);
 }