Lab4-Heap: The dut deasserts full after a remove operation has finished on a previously full dut

In [HeapControl.scala](https://github.com/schoeberl/chisel-lab/blob/master/lab4/src/main/scala/heap/HeapControl.scala#L47), using `RegEnable` will make full always be true after the first time when heap is full, so the dut cannot deassert full after a remove operation has finished on a previously full dut?