Cleanup public plugins metadata

Summary: Now we support splitting metadata to public and fb-internal (see the previous diff in the stack), and this diff actually cleans up all public plugin metadata from fb-specific things.

Reviewed By: passy

Differential Revision: D28568413

fbshipit-source-id: eae699eabaae489c4bcfbfcc407c3bef42bfd338

desktop/plugins/public/example/package.json

@@ -13,7 +13,7 @@
   "title": "Example Plugin",
   "icon": "apps",
   "bugs": {
-    "url": "https://fbflipper.com/"
+    "url": "https://github.com/facebook/flipper/issues"
   },
   "scripts": {
     "lint": "flipper-pkg lint",