By default, iOS safari will automatically zoom into focused inputs with
font-sizes less than 16px. To avoid this, we had a CSS rule to ensure
inputs always had a large font-size on iOS. This worked, but did lead to
design inconsistencies.
Instead, we can set `user-scalable=no` on the viewport meta tag. Since
iOS 10, this property doesn't actually stop users zooming. But it *does*
still prevent the automatic zooming of inputs. So it solves our zoom
problem, and allows us to remove the CSS font-size workaround.
c171e3dccd