Auto merge of #106981 - joboet:std_remove_box_syntax, r=thomcc

Do not use box syntax in `std`

See #94970 and #49733. About half of the `box` instances in `std` do not even need to allocate, the other half can simply be replaced with `Box::new`.

`@rustbot` label +T-libs
r? rust-lang/libs

Author: bors