Some files already were using `noop` in place of `() => {}`.
It's both clearer what it means and is easier to type.
This updates all test files to fully use `noop`, and
adds a shared import from the test lib file.
This switches to our preferred dash-separated classnames
instead of underscore-separated, and also updates the
classname to be differentiable from users that aren't
part of the current narrow.
Until the next commit that splits the buddy list, the
name is a bit inaccurate since it still contains all
the users.
This lets us simplify the long-ish ‘../../static/js’ paths, and will
remove the need for the ‘zrequire’ wrapper.
Signed-off-by: Anders Kaseorg <anders@zulip.com>