fix some harmless compiler warnings

this comes with a minor API change as well, as the FaultCollection
class did not use the Cartesian size of the grid at all, so I decided
to remove the attributes and the arguments to the constructor...

opm/parser/eclipse/EclipseState/Grid/FaultCollection.cpp

@@ -23,10 +23,7 @@
 
 namespace Opm {
 
-    FaultCollection::FaultCollection(size_t nx , size_t ny , size_t nz) :
-        m_nx(nx),
-        m_ny(ny),
-        m_nz(nz)
+    FaultCollection::FaultCollection()
     {
         
     }