Simplify os_str_bytes cfg expression.
Simplify os_str_bytes cfg expression.

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