[FLINK-14859][runtime] Remove wrong checkState

A slot that is assigned to an execution may be unreleased even if a deployment
is outdated. However, this is safe, because the execution is responsible for
releasing the slot.

This closes apache#10351.

flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/DefaultScheduler.java

@@ -440,12 +440,6 @@ private BiFunction<Object, Throwable, Void> deployOrHandleError(final Deployment
 
  return (ignored, throwable) -> {
  if (executionVertexVersioner.isModified(requiredVertexVersion)) {
- final boolean slotAlive = deploymentHandle
- .getLogicalSlot()
- .map(LogicalSlot::isAlive)
- .orElse(false);
- checkState(!slotAlive, "Expected slot to be released");
-
  log.debug("Refusing to deploy execution vertex {} because this deployment was " +
  "superseded by another deployment", executionVertexId);
  return null;