log: remove LOG_TARGET_SAFE pseudo log target

This removes LOG_TARGET_SAFE. It's made redundant by the new
"prohibit-ipc" logging flag, as it used to have a similar effect: avoid
logging to the journal/syslog, i.e. any local services in order to avoid
deadlocks when we lock from PID 1 or its utility processes (such as
generators).

All previous users of LOG_TARGET_SAFE are switched over to the new
setting. This makes things a bit safer for all, as not even the
SYSTEMD_LOG_TARGET env var can be used to accidentally log to the
journal anymore in these programs.

src/debug-generator/debug-generator.c

@@ -165,7 +165,8 @@ int main(int argc, char *argv[]) {
         if (argc > 1)
                 arg_dest = argv[2];
 
-        log_set_target(LOG_TARGET_SAFE);
+        log_set_prohibit_ipc(true);
+        log_set_target(LOG_TARGET_AUTO);
         log_parse_environment();
         log_open();