Rollup merge of #44840 - steveklabnik:fix-wording, r=BurntSushi
Rollup merge of #44840 - steveklabnik:fix-wording, r=BurntSushi

Improve wording for StepBy

No other iterator makes the distinction between an iterator and an iterator adapter
in its summary line, so change it to be consistent with all other adapters.

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