[ios] Disables OpenInManagerTest.testOpenIn on tablet.

The test does not currently work when the share menu displays in a
popover.

BUG=983135

Change-Id: I6d9e106792b4bb383b257fd6b315e62a0fdddc23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1698122
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676427}