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_os2.c b/Python/dynload_os2.c
index f7264da..0e1b907 100644
--- a/Python/dynload_os2.c
+++ b/Python/dynload_os2.c
@@ -9,11 +9,7 @@
 #include "importdl.h"
 
 
-const struct filedescr _PyImport_DynLoadFiletab[] = {
-    {".pyd", "rb", C_EXTENSION},
-    {".dll", "rb", C_EXTENSION},
-    {0, 0}
-};
+const char *_PyImport_DynLoadFiletab[] = {".pyd", ".dll", NULL};
 
 dl_funcptr _PyImport_GetDynLoadFunc(const char *shortname,
                                     const char *pathname, FILE *fp)