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

Revert Vec/Rc storage reuse opt

Remove the optimization for using storage added by rust-lang#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. (rust-lang#104565, rust-lang#104563)

cc `@RalfJung` `@matthiaskrgr`

Fixes rust-lang#104565
Fixes rust-lang#104563

Author: bors