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/imp.py b/Lib/imp.py
index f35247c..0388d08 100644
--- a/Lib/imp.py
+++ b/Lib/imp.py
@@ -94,7 +94,7 @@
 
 
 class _LoadCompiledCompatibility(_HackedGetData,
-        _bootstrap._SourcelessFileLoader):
+        _bootstrap.SourcelessFileLoader):
 
     """Compatibility support for implementing load_compiled()."""