diff: Remove location modification from 2004

diffutils has been carrying this modification since version 2.8.1.  That
version was changed to support libgnuregex which has since been removed.

It appears that likely libgnuregex didn't support the
RE_NO_POSIX_BACKTRACKING option, and thus required the modification.

contrib/diffutils/src/diff.c

@@ -282,7 +282,7 @@ main (int argc, char **argv)
   c_stack_action (0);
   function_regexp_list.buf = &function_regexp;
   ignore_regexp_list.buf = &ignore_regexp;
-  re_set_syntax (RE_SYNTAX_GREP);
+  re_set_syntax (RE_SYNTAX_GREP | RE_NO_POSIX_BACKTRACKING);
   excluded = new_exclude ();
 
   /* Decode the options.  */