libsystemd: drop unexported sd-utf8

It had two symbols which were not actually exported because they were not
listed in libsystemd.sym. They were also entirely unused in our codebase.
I don't think it makes much sense to export just those two functions, and
it doesn't make to build a string processing library in systemd either.

History of the file shows that it was created in
faaa5728d9 'utf8: export utf8 validation functions as part of sd-bus'
and hasn't gone even one non-trivial change since then ;)

src/libsystemd/meson.build

@@ -155,7 +155,6 @@ libsystemd_sources = files(
         'sd-path/sd-path.c',
         'sd-resolve/resolve-private.h',
         'sd-resolve/sd-resolve.c',
-        'sd-utf8/sd-utf8.c',
 ) + sd_journal_sources + id128_sources + sd_daemon_sources + sd_event_sources + sd_login_sources
 
 

src/libsystemd/sd-utf8/sd-utf8.c

@@ -1,18 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-
-#include "sd-utf8.h"
-
-#include "utf8.h"
-#include "util.h"
-
-_public_ const char *sd_utf8_is_valid(const char *s) {
-        assert_return(s, NULL);
-
-        return utf8_is_valid(s);
-}
-
-_public_ const char *sd_ascii_is_valid(const char *s) {
-        assert_return(s, NULL);
-
-        return ascii_is_valid(s);
-}

src/systemd/meson.build

@@ -36,7 +36,6 @@ _not_installed_headers = [
         'sd-network.h',
         'sd-radv.h',
         'sd-resolve.h',
-        'sd-utf8.h',
 ]
 
 install_headers(