Simplify allocator usage in unordered containers

Simplify allocator usage in unordered containers

	* include/bits/hashtable_policy.h (_ReuseOrAllocNode): Remove
	__value_alloc_type and __value_alloc_traits typedefs.
	(_ReuseOrAllocNode::operator()): Call construct and destroy on the
	node allocator.
	(_Hashtable_alloc): Simplify __value_alloc_traits typedef.
	(_Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&&...)): Call
	construct on the node allocator.
	(_Hashtable_alloc<_NodeAlloc>::_M_deallocate_node(__node_type*)): Call
	destroy on the node allocator.

From-SVN: r251187