chore: drop unused dev dependency

Author: nikku

package-lock.json

@@ -79,7 +79,6 @@
     "camunda-bpmn-js-behaviors": "^1.2.1",
     "camunda-bpmn-moddle": "^7.0.1",
     "chai": "^4.3.10",
-    "copy-webpack-plugin": "^11.0.0",
     "cross-env": "^7.0.3",
     "diagram-js": "^12.3.0",
     "downloadjs": "^1.4.7",