Remove Unused Snapshot Status Values

This is a left-over from before elastic#41940 when we used the same status enum for the shards
and the snapshots overall. The two removed values were never used on the shard level
so we can simply remove them here.

server/src/main/java/org/elasticsearch/cluster/SnapshotsInProgress.java

@@ -427,9 +427,7 @@ public enum State {
         STARTED((byte) 1, false),
         SUCCESS((byte) 2, true),
         FAILED((byte) 3, true),
-        ABORTED((byte) 4, false),
-        MISSING((byte) 5, true),
-        WAITING((byte) 6, false);
+        ABORTED((byte) 4, false);
 
         private final byte value;
 
@@ -460,10 +458,6 @@ public static State fromValue(byte value) {
                     return FAILED;
                 case 4:
                     return ABORTED;
-                case 5:
-                    return MISSING;
-                case 6:
-                    return WAITING;
                 default:
                     throw new IllegalArgumentException("No snapshot state for value [" + value + "]");
             }