Rollup merge of #137922 - Zalathar:sharded, r=SparrowLii

A few cleanups after the removal of `cfg(not(parallel))`

I noticed a few small things that are no longer needed after the removal of `cfg(not(parallel))` in #132282.

One of the later changes adjusts several imports, so viewing the changes individually is recommended.

r? SparrowLii (or reroll)

Author: matthiaskrgr