[iOS][OpenIn] Uses system font for the 'Tap to cancel.' label

This CL replaces the font for the 'Tap to cancel' label.

Bug: 1146347
Change-Id: I0e7922f7fb71c5e6d23c65781677f66b734a1810
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523031


Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Auto-Submit: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824834}