bpo-29240: Ignore UTF-8 Mode in time module (#5148)

time.strftime() must use the current LC_CTYPE encoding, not UTF-8
if the UTF-8 mode is enabled.

Add _PyUnicode_DecodeCurrentLocale() function.

Modules/readline.c

@@ -138,8 +138,7 @@ encode(PyObject *b)
 static PyObject *
 decode(const char *s)
 {
-    return _PyUnicode_DecodeCurrentLocaleAndSize(s, strlen(s),
-                                                 "surrogateescape");
+    return _PyUnicode_DecodeCurrentLocale(s, "surrogateescape");
 }