libutil/file-system: make AutoDelete not copyable and movable

Such a RAII structure should NEVER be copyable or movable, otherwise:

```
AutoDelete x;

x = AutoDelete(p, false);
```

will trigger the immediate deletion of `p`!

This fixes an annoying bug where the state record for cgroups was
deleted immediately as soon as it was created.

Change-Id: I2bfbc0815706700a0a75b79d1059cc552119b2c9
Signed-off-by: Raito Bezarius <raito@lix.systems>

lix/libutil/cgroup.cc

@@ -330,7 +330,7 @@ void AutoDestroyCgroup::cleansePreviousInstancesAndRecordOurself(
     }
 
     writeFile(cgroupFile, std::get<std::filesystem::path>(cgroup_).string());
-    stateRecord = AutoDelete(cgroupFile, false);
+    stateRecord.reset(cgroupFile, false);
 }
 
 void AutoDestroyCgroup::adoptProcess(int pid)

lix/libutil/file-system.hh

@@ -273,6 +273,8 @@ class AutoDelete
     bool del;
     bool recursive;
 public:
+    KJ_DISALLOW_COPY_AND_MOVE(AutoDelete);
+
     AutoDelete();
     AutoDelete(const Path & p, bool recursive = true);
     ~AutoDelete();