Other browsers do not support any of these (IIRC), telemetry reports
essentially zero usage, and supporting them is contrary to the DOM spec.
Notes on specific events:
CommandEvent and SimpleGestureEvent: These are not supposed to be
web-exposed APIs, so I hid the interfaces from web content too
(necessary to avoid test_all_synthetic_events.html failures).
DataContainerEvent: This was a non-standard substitute for CustomEvent
that seemed to have only one user, so I removed it entirely and switched
the user (MozillaFileLogger.js) to CustomEvent.
ScrollAreaEvent: This is entirely non-standard, but we apparently expose
it deliberately to web content, so I didn't see any reason to remove it
from createEvent.
SimpleGestureEvent and XULCommandEvent: Can still be created from
createEvent(), but not by content.
TimeEvent: This is still in because it has no constructor, so there's no
other way to create it. Ideally we'd update the SMIL spec to add a
constructor. I did remove TimeEvents.
MozReview-Commit-ID: 7Yi2oCl9SM2
