notes: rename to load_display_notes()

notes: rename to load_display_notes()

According to the function comment, init_display_notes() was supposed to
"Load the notes machinery for displaying several notes trees." Rename
this function to load_display_notes() so that its use is more accurately
represented.

This is done because, in a future commit, we will reuse the name
init_display_notes().

Signed-off-by: Denton Liu <redacted>
Signed-off-by: Junio C Hamano <redacted>