libsystemd: drop unused header

Follow-up for 2dbf1c0f15.

src/systemd/sd-utf8.h

@@ -1,29 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-#ifndef foosdutf8hfoo
-#define foosdutf8hfoo
-
-/***
-  systemd is free software; you can redistribute it and/or modify it
-  under the terms of the GNU Lesser General Public License as published by
-  the Free Software Foundation; either version 2.1 of the License, or
-  (at your option) any later version.
-
-  systemd is distributed in the hope that it will be useful, but
-  WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-  Lesser General Public License for more details.
-
-  You should have received a copy of the GNU Lesser General Public License
-  along with systemd; If not, see <https://www.gnu.org/licenses/>.
-***/
-
-#include "_sd-common.h"
-
-_SD_BEGIN_DECLARATIONS;
-
-_sd_pure_ const char *sd_utf8_is_valid(const char *s);
-_sd_pure_ const char *sd_ascii_is_valid(const char *s);
-
-_SD_END_DECLARATIONS;
-
-#endif