Remove insignificant notes from CStr documentation
Remove insignificant notes from CStr documentation

These notes are about a distinction that is not going to be observable
in the API. Whether or not the UTF-8 check knows the string length ahead
of time, these methods require linear time.

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