Fix compilation warning: type qualifier ignored

```cpp
Software/DGtal/DGtal-src/src/DGtal/base/OrderedAlphabet.ih:594:60: warning: type qualifiers ignored on cast result type [-Wignored-qualifiers]
   ModuloComputer< Integer > mc( (const unsigned int)w.size() );
```

src/DGtal/base/OrderedAlphabet.ih

@@ -591,7 +591,7 @@ DGtal::OrderedAlphabet::nextEdge( size_t & nb_a1,
             index_t & s,
             bool & cvx )
 {
-  ModuloComputer< Integer > mc( (const unsigned int)w.size() );
+  ModuloComputer< Integer > mc( (unsigned int)w.size() );
   size_t l;
   size_t len;
   size_t nb;