Cluster: no limits for the count parameter of CLUSTER GETKEYSINSLOT.

Not sure why I set a limit to 1 million keys, there is no reason for
this artificial limit, and anyway this is s a stupid limit because it is
already high enough to create latency issues. So let's the users shoot
on their feet because maybe they just actually know what they are doing.

src/cluster.c

@@ -1659,8 +1659,7 @@ void clusterCommand(redisClient *c) {
             return;
         if (getLongLongFromObjectOrReply(c,c->argv[3],&maxkeys,NULL) != REDIS_OK)
             return;
-        if (slot < 0 || slot >= REDIS_CLUSTER_SLOTS || maxkeys < 0 ||
-            maxkeys > 1024*1024) {
+        if (slot < 0 || slot >= REDIS_CLUSTER_SLOTS || maxkeys < 0) {
             addReplyError(c,"Invalid slot or number of keys");
             return;
         }