notes: move the notes name argument

Make it consistent between git_note_create() and git_note_remote() by
putting it after the repository.
notes: fix comments for git_note_next()

The iterator is the last argument. There is also no returned notes, just
ids, so the comment about freeing is out of place.
Merge pull request #2747 from libgit2/cmn/notes-consistency

Notes API consistency fixes