Missing action: clear

[cm-t 🦄🏂🌈🎵]

I am reading a notification on the watch.
I now want to be sure I won't have to read it again on the phone.
I should be able to clear a notification I've read from the watch to the phone(probably using a notification action "mark as read on the phone's notification area" on the watch )

[Andrew Branson (abranson)]

The dismiss action should do this, but until my last merge those actions weren't notifying the phone. I've got more support in the platform interface for this, because it works in Rockpool. I'll push those changes through.