pid1: rework environment block copy logic

This reworks the logic introduced in
a5cede8c24 (#13693).

First of all, let's move this out of util.c, since only PID 1 really
needs this, and there's no real need to have it in util.c.

Then, fix freeing of the variable. It previously relied on
STATIC_DESTRUCTOR_REGISTER() which however relies on static_destruct()
to be called explicitly. Currently only the main-func.h macros do that,
and PID 1 does not. (It might be worth investigating whether to do that,
but it's not trivial.) Hence the freeing wasn't applied.

Finally, an OOM check was missing, add it in.

src/basic/util.c

@@ -38,7 +38,6 @@
 #include "set.h"
 #include "signal-util.h"
 #include "stat-util.h"
-#include "static-destruct.h"
 #include "string-util.h"
 #include "strv.h"
 #include "time-util.h"
@@ -49,11 +48,8 @@
 
 int saved_argc = 0;
 char **saved_argv = NULL;
-char **saved_env = NULL;
 static int saved_in_initrd = -1;
 
-STATIC_DESTRUCTOR_REGISTER(saved_env, strv_freep);
-
 bool kexec_loaded(void) {
        _cleanup_free_ char *s = NULL;
 
@@ -301,7 +297,3 @@ void disable_coredumps(void) {
         if (r < 0)
                 log_debug_errno(r, "Failed to turn off coredumps, ignoring: %m");
 }
-
-void save_env(void) {
-        saved_env = strv_copy(environ);
-}