Remove Preview Flag (#133)

To comply with policy.

Co-authored-by: Gabe Stocco <gstocco@microsoft.com>

DevSkim-VSCode-Plugin/package.json

@@ -5,7 +5,6 @@
   "author": "Microsoft Corporation",
   "license": "MIT",
   "version": "0.0.0-placeholder",
-  "preview": true,
   "publisher": "MS-CST-E",
   "repository": {
     "type": "git",