[ios] Fix imports in bvc

This CL removes unnecessary imports and forward declarations from the
header file, and move them to the necessary implementation files.

Change-Id: If6e41ffe9d85d063f2b14e4c74b12b06b46261b7
Reviewed-on: https://chromium-review.googlesource.com/c/1370581
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615565}
6 files changed