Auto merge of #104571 - clubby789:remove-vec-rc-opt, r=the8472

Revert Vec/Rc storage reuse opt

Remove the optimization for using storage added by #104205.
The perf wins were pretty small, and it relies on non-guarenteed behaviour. On platforms that don't implement shrinking in place, the performance will be significantly worse.

While it could be gated to platforms that do this (such as GNU), I don't think it's worth the overhead of maintaining it for very small gains. (#104565, #104563)

cc `@RalfJung` `@matthiaskrgr`

Fixes #104565
Fixes #104563

Author: bors