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#104565Fixes#104563