Performance lib public method tweak (#1310)
Performance lib public method tweak (#1310)

* Removed log statement that prints too frequently, and replaced it with a
count of the delete notes for the transpose function in sequences_lib.py

* Fixed lint errors hopefully.

* Fixed typo in comment.

* Make velocity_to_bin and velocity_bin_to_velocity methods public.

magenta/note-seq,magenta/note-seq,magenta/note-seq