remove some duplication

Objects/unicodeobject.c

@@ -2838,6 +2838,10 @@ normalize_encoding(const char *encoding,
     char *l;
     char *l_end;
 
+    if (encoding == NULL) {
+        strcpy(lower, "utf-8");
+        return 1;
+    }
     e = encoding;
     l = lower;
     l_end = &lower[lower_len - 1];
@@ -2869,9 +2873,6 @@ PyUnicode_Decode(const char *s,
     Py_buffer info;
     char lower[11];  /* Enough for any encoding shortcut */
 
-    if (encoding == NULL)
-        return PyUnicode_DecodeUTF8(s, size, errors);
-
     /* Shortcuts for common default encodings */
     if (normalize_encoding(encoding, lower, sizeof(lower))) {
         if ((strcmp(lower, "utf-8") == 0) ||
@@ -3101,13 +3102,6 @@ PyUnicode_AsEncodedString(PyObject *unicode,
         return NULL;
     }
 
-    if (encoding == NULL) {
-        if (errors == NULL || strcmp(errors, "strict") == 0)
-            return _PyUnicode_AsUTF8String(unicode, NULL);
-        else
-            return _PyUnicode_AsUTF8String(unicode, errors);
-    }
-
     /* Shortcuts for common default encodings */
     if (normalize_encoding(encoding, lower, sizeof(lower))) {
         if ((strcmp(lower, "utf-8") == 0) ||