incron state: rm unused imports

```
************* Module salt.states.incron
salt/states/incron.py:44: [W0611(unused-import), ] Unused import os
salt/states/incron.py:47: [W0611(unused-import), ] Unused import salt
salt/states/incron.py:49: [W0611(unused-import), ] Unused import _needs_change
```