Function remove_duplicates 

pub fn remove_duplicates<T, F>(arr: &mut [T], equal: &F) -> usize
where
    T: Copy,
    F: Fn(&T, &T) -> bool,

Remove duplicates from a sorted slice. Returns the number of remaining elements. The slice is modified in place (duplicates are overwritten, tail is unchanged).

Port of C++ remove_duplicates.