Rollup merge of #55127 - ljedrz:simplify_hybridbitset, r=matthewjasper
Rollup merge of #55127 - ljedrz:simplify_hybridbitset, r=matthewjasper

Remove HybridBitSet::dummy

This simplifies some of the `HybridBitSet` code.

cc @nnethercote

aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust