Delete all chunk_file when they merged

lib/whaleback/chunk_file.rb

@@ -58,7 +58,10 @@ module Whaleback
         file.write(@file&.read)
       end
       finish_loading
-      merge_file if all_finish?
+      if all_finish?
+        merge_file
+        all_suicide
+      end
     end
 
     def merge_file
@@ -80,6 +83,10 @@ module Whaleback
       )
     end
     
+    def all_suicide
+      ChunkFile.where(identifier: identifier).destroy_all
+    end
+
     # 可覆盖，Obj class 继承有 STI type 问题，也可以细化分类
     def assign_media_class mime_type
       case mime_type