bpo-30167: Remove __cached__ from __main__ when removing __file__ (GH-7415)

Misc/NEWS.d/next/Core and Builtins/2018-06-05-15-49-02.bpo-30167.e956hA.rst

+``PyRun_SimpleFileExFlags`` removes ``__cached__`` from module in addition
+to ``__file__``.

Python/pythonrun.c

@@ -434,8 +434,14 @@ PyRun_SimpleFileExFlags(FILE *fp, const char *filename, int closeit,
     Py_DECREF(v);
     ret = 0;
   done:
-    if (set_file_name && PyDict_DelItemString(d, "__file__"))
-        PyErr_Clear();
+    if (set_file_name) {
+        if (PyDict_DelItemString(d, "__file__")) {
+            PyErr_Clear();
+        }
+        if (PyDict_DelItemString(d, "__cached__")) {
+            PyErr_Clear();
+        }
+    }
     Py_XDECREF(m);
     return ret;
 }