libstdc++: Fold some ranges algo subroutines into their only caller

libstdc++: Fold some ranges algo subroutines into their only caller

These subroutines have only a single call site, so it might be best and simplest
to eliminate them before we convert the algos into function objects.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algo.h (ranges::__find_end): Fold into ...
	(ranges::find_end): ... here.
	(ranges::__lexicographical_compare): Fold into ...
	(ranges::lexicographical_compare): ... here.
	* include/bits/ranges_algobase.h (ranges::__equal): Fold into ...
	(ranges::equal): ... here.