Remove system property es.enforce_max_shards_per_node (#36968)

The system property es.enforce_max_shards_per_node was not needed any more,
because we always enforce cluster-wide shard limit now.

server/src/main/java/org/elasticsearch/indices/IndicesService.java

@@ -159,20 +159,6 @@ public class IndicesService extends AbstractLifecycleComponent
     public static final String INDICES_SHARDS_CLOSED_TIMEOUT = "indices.shards_closed_timeout";
     public static final Setting<TimeValue> INDICES_CACHE_CLEAN_INTERVAL_SETTING =
         Setting.positiveTimeSetting("indices.cache.cleanup_interval", TimeValue.timeValueMinutes(1), Property.NodeScope);
-    private static final boolean ENFORCE_MAX_SHARDS_PER_NODE;
-
-    static {
-        final String ENFORCE_SHARD_LIMIT_KEY = "es.enforce_max_shards_per_node";
-        final String enforceMaxShardsPerNode = System.getProperty(ENFORCE_SHARD_LIMIT_KEY);
-        if (enforceMaxShardsPerNode == null) {
-            ENFORCE_MAX_SHARDS_PER_NODE = false;
-        } else if ("true".equals(enforceMaxShardsPerNode)) {
-            ENFORCE_MAX_SHARDS_PER_NODE = true;
-        } else {
-            throw new IllegalArgumentException(ENFORCE_SHARD_LIMIT_KEY + " may only be unset or set to [true] but was [" +
-                enforceMaxShardsPerNode + "]");
-        }
-    }
 
     /**
      * The node's settings.