launcher-logind: Remove systemd-logind support

Many years ago (2014) systemd-logind was brought into libsystemd.
We've supported old versions of systemd-logind ever since.

Let's remove support for old versions of systemd-logind before the
merge for a tiny code simplification.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

libweston/launcher-logind.c

@@ -695,29 +695,6 @@ launcher_logind_release_control(struct launcher_logind *wl)
 	}
 }
 
-static int
-weston_sd_session_get_vt(const char *sid, unsigned int *out)
-{
-#ifdef HAVE_SYSTEMD_LOGIN_209
-	return sd_session_get_vt(sid, out);
-#else
-	int r;
-	char *tty;
-
-	r = sd_session_get_tty(sid, &tty);
-	if (r < 0)
-		return r;
-
-	r = sscanf(tty, "tty%u", out);
-	free(tty);
-
-	if (r != 1)
-		return -EINVAL;
-
-	return 0;
-#endif
-}
-
 static int
 launcher_logind_activate(struct launcher_logind *wl)
 {
@@ -803,7 +780,7 @@ launcher_logind_connect(struct weston_launcher **out, struct weston_compositor *
 	r = sd_seat_can_tty(t);
 	free(t);
 	if (r > 0) {
-		r = weston_sd_session_get_vt(wl->sid, &wl->vtnr);
+		r = sd_session_get_vt(wl->sid, &wl->vtnr);
 		if (r < 0) {
 			weston_log("logind: session not running on a VT\n");
 			goto err_session;

libweston/meson.build

@@ -156,13 +156,8 @@ endif
 systemd_dep = dependency('', required: false)
 if get_option('launcher-logind')
 	systemd_dep = dependency('libsystemd', version: '>= 209', required: false)
-	if systemd_dep.found()
-		config_h.set('HAVE_SYSTEMD_LOGIN_209', '1')
-	else
-		systemd_dep = dependency('libsystemd-login', version: '>= 198', required: false)
-		if not systemd_dep.found()
-			error('logind support requires libsystemd or libsystemd-login but neither was found. Or, you can use \'-Dlauncher-logind=false\'')
-		endif
+	if not systemd_dep.found()
+		error('logind support requires libsystemd >= 209. Or, you can use \'-Dlauncher-logind=false\'')
 	endif
 
 	dbus_dep = dependency('dbus-1', version: '>= 1.6', required: false)