Remove fillLimit rule and its migration code

It has been replaced by the `commandModificationBlockLimit` gamerule

src/main/java/carpet/script/external/Vanilla.java

@@ -346,7 +346,7 @@ public class Vanilla
 
     public static int MinecraftServer_getFillLimit(MinecraftServer server)
     {
-        return Math.max(server.getGameRules().getInt(GameRules.RULE_COMMAND_MODIFICATION_BLOCK_LIMIT), CarpetSettings.fillLimit);
+        return server.getGameRules().getInt(GameRules.RULE_COMMAND_MODIFICATION_BLOCK_LIMIT);
     }
 
     public static int PoiRecord_getFreeTickets(PoiRecord record)