Fix open source .pyre_configuration file (#104)

Summary:

The open source pyre configuration is broken.
This is causing Github CI errors: `Invalid configuration: Invalid path ujson: does not exist.`

Differential Revision: D49093816

.pyre_configuration

@@ -3,58 +3,8 @@
     "setup.py",
     "stubs"
   ],
+  "site_package_search_strategy": "pep561",
   "search_path": [
-    {
-      "site-package": "click"
-    },
-    {
-      "site-package": "click_log"
-    },
-    {
-      "site-package": "flask"
-    },
-    {
-      "site-package": "flask_graphql"
-    },
-    {
-      "site-package": "graphql"
-    },
-    {
-      "site-package": "graphene"
-    },
-    {
-      "site-package": "graphene_sqlalchemy"
-    },
-    {
-      "site-package": "IPython"
-    },
-    {
-      "site-package": "munch"
-    },
-    {
-      "site-package": "pygments"
-    },
-    {
-      "site-package": "ujson"
-    },
-    {
-      "site-package": "xxhash"
-    },
-    {
-      "site-package": "prompt_toolkit"
-    },
-    {
-      "site-package": "traitlets"
-    },
-    {
-      "site-package": "typing_extensions"
-    },
-    {
-      "site-package": "pyre_extensions"
-    },
-    {
-      "site-package": "flask_cors"
-    },
     "stubs"
   ],
   "source_directories": [