Noticed GRAPH_MT_channel_context_menu is unused (since
DOPESHEET_MT_channel_context_menu is used in both Dopesheet & Graph/
Drivers Editor).
This patch removes GRAPH_MT_channel_context_menu but adds the entries
which were in that menu (but not in DOPESHEET_MT_channel_context_menu)
back to the later.
Namely:
- Hide Selected Curves
- Hide Unselected Curves
- Reveal Curves
- (Delete Invalid Drivers -- if in Drivers Editor)
Philipp Oeser