This wasn't being used by osu-web, and included far too much unnecessary
data. Of note, `pp` and `ruleset_id` are also not strictly required, but
there's no harm in sending them so I've left them be for now.
`currentChannel` gets instantiated once the chat overlay is open, while
`HighlightMessage` could be called while the chat overlay has never been
open.
This will all be rewritten with the new chat overlay design anyways, so
should be fine for now.
I kinda liked this flow, but from multiple reports from users it
definitely seems in the way. We can revisit after the new design is
applied to song select.
Note that this means the tooltips also don't display. If it is preferred
that they should (arguable from a UX perspective, since I'd expect to be
able to click at that point) then the issue can be addressed using a
slightly different path (a few more lines - nothing too complex).