Removed ex-employees as PoC

Summary:
When creating the plugin overview (https://docs.google.com/spreadsheets/d/181jKpsUHO3q8I1G-bMcu-O7Hr3f4GCDVXKMVY2beOuQ/edit?usp=sharing) found some plugins with inactive points of contact

Per title, having no PoC entry makes it more clear there is none, rather than having an ex-employee in there that can't be reached

Reviewed By: nikoant

Differential Revision: D24783043

fbshipit-source-id: a852f87f42350476558bc9fc67cb3ad427268a2f

desktop/plugins/leak_canary/package.json

@@ -14,6 +14,6 @@
   "icon": "bird",
   "title": "LeakCanary",
   "bugs": {
-    "email": "jhli@fb.com"
+    "email": ""
   }
 }