The antialiasing decisions we made for the webapp should be constant
over the entire page, not limited to particular subsections or themes.
If we wanted antialiasing, we should do it on the entire page, not
individual random widgets. But it's not clear we actually want to do
it on the entire page. The `-moz-osx-font-smoothing: grayscale`
setting now happens by default in OSX Mojave (40% world market share
right now and growing), so there's no reason to override it. And
without retina displays, generally, subpixel rendering provides better
results than antialiasing (which overrides subpixel rendering).
Thanks to Anders Kaseorg for advice on this issue.