Allocator template parameter of classes without memory management

Several classes in bvector.hh and basearray.hh have an allocator template parameter but don't do any memory management. This is true for base_array_unmanaged, base_array_window, compressed_base_array_unmanaged, block_vector_unmanaged, BlockVectorWindow, compressed_block_vector_unmanaged, CompressedBlockVectorWindow.