add clean script

packages/backend/package.json

@@ -59,7 +59,6 @@
 		"@types/redis": "2.8.32",
 		"@types/rename": "1.0.4",
 		"@types/request-stats": "3.0.0",
-		"@types/rimraf": "3.0.2",
 		"@types/seedrandom": "2.4.28",
 		"@types/sharp": "0.29.3",
 		"@types/sinonjs__fake-timers": "6.0.4",
@@ -162,7 +161,6 @@
 		"rename": "1.0.4",
 		"request-stats": "3.0.0",
 		"require-all": "3.0.0",
-		"rimraf": "3.0.2",
 		"rndstr": "1.0.0",
 		"s-age": "1.1.2",
 		"seedrandom": "3.0.5",