Backout ab500b297900: the check for integer overflow is wrong

Issue #14716: Change integer overflow check in unicode_writer_prepare()
to compute the limit at compile time instead of runtime. Patch writen by Serhiy
Storchaka.

Objects/unicodeobject.c

@@ -13242,10 +13242,8 @@ unicode_writer_prepare(unicode_writer_t *writer,
     newlen = writer->pos + length;
 
     if (newlen > PyUnicode_GET_LENGTH(writer->buffer)) {
-        /* Overallocate 25% to limit the number of resize.
-           Check for integer overflow:
-           (newlen + newlen / 4) <= PY_SSIZE_T_MAX */
-        if (newlen <= (PY_SSIZE_T_MAX - PY_SSIZE_T_MAX / 5))
+        /* overallocate 25% to limit the number of resize */
+        if (newlen <= (PY_SSIZE_T_MAX - newlen / 4))
             newlen += newlen / 4;
 
         if (maxchar > writer->maxchar) {