libstdc++: Remove unnecessary header from <memory>

libstdc++: Remove unnecessary header from <memory>

Previously <memory> included <bits/stl_algobase.h> so that std::copy,
std::fill etc. could be used by <bits/stl_uninitialized.h>. But that
includes it explicitly now, so that it can be compiled as a header unit.
There's no need to include it in <memory>, where its purpose isn't
obvious.

libstdc++-v3/ChangeLog:

	* include/std/memory: Do not include <bits/stl_algobase.h>.