[NFC][libc++] Update comments to reflect changes in ASan

ASan capabilities were extended, but some comments were not updated and describe old behavior. This commit updates outdated comments, which I found.
Mentioned changes are:
- All allocators in containers (`std::vector` and `std::deque`; D146815 D136765) are supported, but it's possible to turn off annotations for a specific allocator (D145628).
- Buffers don't have to be aligned (D132522).

Reviewed By: #libc, philnik

Differential Revision: https://reviews.llvm.org/D156155