chore(deps): remove deprecated @slack/events-api package

Author: hivanalejandro

functions/slack/package.json

@@ -16,8 +16,7 @@
   },
   "dependencies": {
     "@google-cloud/functions-framework": "^3.1.0",
-    "@googleapis/kgsearch": "^1.0.0",
-    "@slack/events-api": "^3.0.0"
+    "@googleapis/kgsearch": "^1.0.0"
   },
   "devDependencies": {
     "c8": "^10.0.0",