snap: do not use os.Environ() in 2.44

The new code in isStopping() is using osutil.OsEnvironment which
is not availalbe yet in snapd 2.44. This commit uses the "old"
way of doing the environment to fix building 2.44.

cmd/snap/cmd_run.go

@@ -115,14 +115,11 @@ and environment.
 // isStopping returns true if the system is shutting down.
 func isStopping() (bool, error) {
 	// Make sure, just in case, that systemd doesn't localize the output string.
-	env, err := osutil.OSEnvironment()
-	if err != nil {
-		return false, err
-	}
-	env["LC_MESSAGES"] = "C"
+	env := os.Environ()
+	env = append(env, "LC_MESSAGESC=C")
 	// Check if systemd is stopping (shutting down or rebooting).
 	cmd := exec.Command("systemctl", "is-system-running")
-	cmd.Env = env.ForExec()
+	cmd.Env = env
 	stdout, err := cmd.Output()
 	// systemctl is-system-running returns non-zero for outcomes other than "running"
 	// As such, ignore any ExitError and just process the stdout buffer.