Remove RawVec::cap()
Remove RawVec::cap()

As suggested in https://github.com/rust-lang/rust/pull/60340#issuecomment-493681032

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