Don't use NSAccessibilityRemoteUIElement for WebContentsViewMac

Using this API may be causing crashes, and it was only added for code
cleanliness. Remove it.

TBR=ccameron@chromium.org, ellyjones

(cherry picked from commit cff221605266947be84c7057c61989c44962e0f7)

Bug: 924955
Change-Id: Id25bab33958381bd16ce4887c842943ccae99a34
Reviewed-on: https://chromium-review.googlesource.com/c/1437395
Commit-Queue: ccameron <ccameron@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#626202}
Reviewed-on: https://chromium-review.googlesource.com/c/1450397
Cr-Commit-Position: refs/branch-heads/3683@{#126}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
4 files changed