core/exec-credential: stop removing empty credentials dir

Starting from cfbf7538d8 we'd always
install the credentials dir regardless of whether it's empty,
with the correct permissions. Hence the problem stated in the comment
should no longer be a concern. Moreover, this ensures later in
setup_namespace() the mountpoint would be in-place. This is important
for credential reloading as it saves the trouble of remounting
the upper tmpfs as rw again and create the mountpoint.

src/core/exec-credential.c

@@ -1145,11 +1145,8 @@ int exec_setup_credentials(
                 return r;
 
         r = setup_credentials_internal(context, cgroup_context, params, unit, p, uid, gid);
+        if (r < 0)
+                (void) rmdir(p);
 
-        /* If the credentials dir is empty and not a mount point, then there's no point in having it. Let's
-         * try to remove it. This matters in particular if we created the dir as mount point but then didn't
-         * actually end up mounting anything on it. In that case we'd rather have ENOENT than EACCESS being
-         * seen by users when trying access this inode. */
-        (void) rmdir(p);
         return r;
 }

src/core/namespace.c

@@ -2845,7 +2845,6 @@ int setup_namespace(const NamespaceParameters *p, char **reterr_path) {
                         .mode = MOUNT_BIND,
                         .read_only = true,
                         .source_const = p->creds_path,
-                        .ignore = true,
                 };
         }