[pyre] use --preserve-pythonpath to enable Pyre to read from site-packages/

.circleci/config.yml

@@ -71,7 +71,7 @@ jobs:
             source /tmp/libcst-env/bin/activate
             pip install --upgrade pip
             pip install -r requirements.txt -r requirements-dev.txt
-            pyre check
+            pyre --preserve-pythonpath check
             PYTHONPATH=`pwd` python libcst/tests/test_pyre_integration.py
             git diff --exit-code  # verify no generated changes
       - save_cache:

setup.py

@@ -6,7 +6,6 @@
 import importlib.util
 from os import path
 
-# pyre-ignore Pyre doesn't know about setuptools.
 import setuptools
 
 

stubs/hypothesmith.pyi

@@ -1 +0,0 @@
-# pyre-placeholder-stub