[kernel] Remove placement-new declaration from memory.h.cog

Finishing the trend of using `#include <new>` to define new, get rid of
the last bits of custom-declared operator new.

src/libraries/util/include/util/vector.h

@@ -2,6 +2,7 @@
 /// \file vector.h
 /// Definition of a simple dynamic vector collection for use in kernel space
 
+#include <new>
 #include <assert.h>
 #include <string.h>
 #include <utility>