[iOS] Remove LegacyFullscreenController.

This is patch 3/3 of a 3-way patch.

Bug: 798064
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I45386c88441ba74b0a16d2fdaf88190a87b79f0f
Reviewed-on: https://chromium-review.googlesource.com/912201
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536205}
3 files changed