Issue #13959: Re-implement imp.get_suffixes() in Lib/imp.py.

This introduces a new function, imp.extension_suffixes(), which is
currently undocumented. That is forthcoming once issue #14657 is
resolved and how to expose file suffixes is decided.
diff --git a/Python/dynload_dl.c b/Python/dynload_dl.c
index a914a08..5836cb3b 100644
--- a/Python/dynload_dl.c
+++ b/Python/dynload_dl.c
@@ -9,10 +9,7 @@
 
 extern char *Py_GetProgramName(void);
 
-const struct filedescr _PyImport_DynLoadFiletab[] = {
-    {".o", "rb", C_EXTENSION},
-    {0, 0}
-};
+const char *_PyImport_DynLoadFiletab[] = {".o", NULL};
 
 
 dl_funcptr _PyImport_GetDynLoadFunc(const char *shortname,