bpo-32030: pass interp to _PyImport_Init() (#4736)

Remove also the initstr variable, unused since the commit
e69f0df45b709c25ac80617c41bbae16f56870fb pushed in 2012: "bpo-13959:
Re-implement imp.find_module() in Lib/imp.py"
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index b615c79..504036c 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -751,7 +751,7 @@
     PySys_SetObject("__stderr__", pstderr);
     Py_DECREF(pstderr);
 
-    err = _PyImport_Init();
+    err = _PyImport_Init(interp);
     if (_Py_INIT_FAILED(err)) {
         return err;
     }