Issue #14605: Rename _SourcelessFileLoader to SourcelessFileLoader.

This time also recreating the Python/importlib.h file to make
make happy. See the ticket for details.
diff --git a/Lib/importlib/abc.py b/Lib/importlib/abc.py
index baa09fd..c171da3 100644
--- a/Lib/importlib/abc.py
+++ b/Lib/importlib/abc.py
@@ -119,7 +119,7 @@
     ExecutionLoader ABCs."""
 
 _register(FileLoader, machinery.SourceFileLoader,
-            machinery._SourcelessFileLoader)
+            machinery.SourcelessFileLoader)
 
 
 class SourceLoader(_bootstrap.SourceLoader, ResourceLoader, ExecutionLoader):