Remove a type signature of 'withBDD'.

This removes a type signature of 'withBDD' in CUDD.chs, because recent version of c2hs automatically generate it and duplication of type signatures cause following compilation error.

```
[1 of 1] Compiling Data.Boolean.CUDD ( dist/build/Data/Boolean/CUDD.hs, dist/build/Data/Boolean/CUDD.o )

Data/Boolean/CUDD.chs:116:1:
    Duplicate type signatures for ‘withBDD’
    at Data/Boolean/CUDD.chs:115:1-7
       Data/Boolean/CUDD.chs:116:1-7
```

The problem is first reported at https://github.com/peteg/hBDD/issues/1 .