[multitypeblockvector.hh] Don't include deprecated allocator.hh.

ISTLAllocator, the only thing provided allocator.hh is not even mentioned in
multitypeblockvector.hh.

[[Imported from SVN: r1302]]

dune/istl/multitypeblockvector.hh

@@ -9,7 +9,6 @@
 #include <iostream>
 
 #include "istlexception.hh"
-#include "allocator.hh"
 
 #include "gsetc.hh"