libstdc++: Cleanup whitespace and type trait usage in <optional>

libstdc++: Cleanup whitespace and type trait usage in <optional>

This makes the formatting in <optional> consistent and also removes
redundant && tokens from template arguments for traits like
is_constructible and is_convertible.

libstdc++-v3/ChangeLog:

	* include/std/optional (_Optional_payload_base, _Optional_base)
	(optional, __optional_hash_call_base): Adjust whitespace and
	other formatting. Remove redundant && tokens on template
	arguments to type traits.