Clarify function comment for `erase` by stating that this idiom only works for "some" standard containers.

If you use this idiom with `std::vector` or `absl::btree_map` you can end up either skipping elements or dereferencing an invalid iterator.

PiperOrigin-RevId: 639892758
Change-Id: Ic5c213667b4b1e8c39813ee237aaffe320a8eb27