fix some masochistic compiler warnings for the GCC 9 pre-release

the flags which I used are
```
-pedantic \
-Wall \
-Wextra \
-Wformat-nonliteral \
-Wcast-align
-Wpointer-arith \
-Wmissing-declarations \
-Wcast-qual \
-Wshadow
-Wwrite-strings \
-Wchar-subscripts \
-Wredundant-decls \
-fstrict-overflow \
-O3 \
-march=native \
-DNDEBUG=1
```

note that some heavy filtering is not the worst idea because DUNE is
far from not emiting any warnings with these flags.

Also, there were some pesky warnings in test_ecl_output which I don't
know how to fix:

```
tests/test_ecl_output.cc:218:73: warning: missing initializer for member ‘Opm::data::Connection::effective_Kh’ [-Wmissing-field-initializers]
```

ebos/eclwriter.hh

@@ -384,7 +384,6 @@ private:
         }
 
         const auto& globalGridView = globalGrid_.leafGridView();
-        typedef typename Grid::LeafGridView GridView;
 #if DUNE_VERSION_NEWER(DUNE_GRID, 2,6)
         typedef Dune::MultipleCodimMultipleGeomTypeMapper<GridView> ElementMapper;
         ElementMapper globalElemMapper(globalGridView, Dune::mcmgElementLayout());
@@ -450,7 +449,6 @@ private:
         int ny = eclState().getInputGrid().getNY();
 
         const auto& globalGridView = globalGrid_.leafGridView();
-        typedef typename Grid::LeafGridView GridView;
 #if DUNE_VERSION_NEWER(DUNE_GRID, 2,6)
         typedef Dune::MultipleCodimMultipleGeomTypeMapper<GridView> ElementMapper;
         ElementMapper globalElemMapper(globalGridView, Dune::mcmgElementLayout());