libstdc++: Simplify std::erase functions for sequence containers

libstdc++: Simplify std::erase functions for sequence containers

This removes the use of std::ref that meant that __remove_if used an
indirection through the reference, which might be a pessimization. Users
can always use std::ref to pass expensive predicates into erase_if, but
we shouldn't do it unconditionally. We can std::move the predicate so
that if it's not cheap to copy and the user didn't use std::ref, then we
try to use a cheaper move instead of a copy.

There's no reason that std::erase shouldn't just be implemented by
forwarding to std::erase_if. I probably should have done that in
r12-4083-gacf3a21cbc26b3 when std::erase started to call __remove_if
directly.

libstdc++-v3/ChangeLog:

	* include/std/deque (erase_if): Move predicate instead of
	wrapping with std::ref.
	(erase): Forward to erase_if.
	* include/std/inplace_vector (erase_if, erase): Likewise.
	* include/std/string (erase_if, erase): Likewise.
	* include/std/vector (erase_if, erase): Likewise.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>