Remove unnecessary typings.

packages/csvviewer/package.json

@@ -42,7 +42,6 @@
     "@phosphor/widgets": "^1.5.0"
   },
   "devDependencies": {
-    "@types/d3-dsv": "~1.0.30",
     "rimraf": "~2.6.2",
     "typescript": "~2.6.2"
   }