libstdc++: Rename _Hashtable _H1, _H2 and _Hash template parameters

libstdc++: Rename _Hashtable _H1, _H2 and _Hash template parameters

Limit our _Hashtable implementation to ranged hash. _H1 is now rename
to _Hash matching the _Hash functor used for unordered containers. _H2
is now renamed to _RangeHash. Former _Hash simply becomes _Unused. Remove
_ExtractKey storage.

libstdc++-v3/ChangeLog:

	* include/bits/hashtable_policy.h (_Hashtable<>): Rename _H1 into _Hash
	_H2 into _RangeHash and _Hash into _Unused.
	(_Hastable_base<>): Likewise.
	(_Map_base<>): Likewise.
	(_Insert_base<>): Likewise.
	(_Insert<>): Likewise.
	(_Rehash_base<>): Likewise.
	(_Local_iterator_base<>): Likewise.
	(_Hash_code_base<>): Likewise.
	(_Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash, false>):
	Remove.
	(_Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash, true>):
	Remove.
	(_Hash_code_base<_Key, _Value, _ExtractKey, _Hash, _RangeHas, _Unused,
	bool>): Remove _Hashtable_ebo_helper<2, _RangeHash> base type..
	(_Hash_code_base<>::_M_bucket_index(const _Key&, __hash_code, size_t)):
	Replace by...
	(_Hash_code_base<>::_M_bucket_index(__hash_code, size_t)): ...this.
	(_Local_iterator<>): Remove _H1 and _H2 template parameters.
	(_Local_const_iterator<>): Likewise.
	(_Equality<>): Likewise.
	(_Map_base<>::operator[](const key_type&): Adapt.
	(_Map_base<>::operator[](key_type&&): Adapt.
	(_Identity::operator()): Add noexcept.
	(_Select1st::operator()): Likewise.
	(_Hash_code_base<>): Remove _Hashtable_ebo_helper<0, _ExtractKey> base
	type.
	(_Hash_code_base::_M_extract): Remove.
	* include/bits/hashtable.h (_Hashtable<>): Remove _H1 and _H2 template
	parameters. Remove _ExtractKey from constructors.
	(_Hashtable<>::_M_insert_unique_node(const key_type&, size_t,
	__hash_code, __node_type*, size_t)): Replace by...
	(_Hashtable<>::_M_insert_unique_node(size_t, __hash_code,
	 __node_type*, size_t)): ...this.
	(_Hashtable<>::_M_insert_muti_node(__node_type*, const key_type&,
	__hash_code, __node_type*)): Replace by...
	(_Hashtable<>::_M_insert_multi_node(__node_type*, __hash_code,
	__node_type*)): ...this.
	(_Hashtable<>::__key_extract): Remove.
	* include/bits/node_handle.h: Adapt.