Revert "Add AtkText support for caret methods and events"

This reverts commit d4ef536f3bbc7835ada954b4385fd5a109147d1c.

Reason for revert: Implicated in a failure of
AXPlatformNodeWinTest.TestRelationTargetsOfType on Win7 Tests (dbg)(1)

https://ci.chromium.org/p/chromium/builders/ci/Win7%20Tests%20%28dbg%29%281%29/75348

Original change's description:
> Add AtkText support for caret methods and events
> 
> Bug: 866338
> Change-Id: I5edb2c94b8ebd0807fec081c593188cbbb672801
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1486231
> Commit-Queue: Martin Robinson <mrobinson@igalia.com>
> Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#639046}

TBR=dmazzoni@chromium.org,mrobinson@igalia.com

Change-Id: Iddc0e74187ac0d37a12c86a60ca8bcc375c7ab51
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 866338
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1511710
Reviewed-by: Robert Liao <robliao@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639137}
9 files changed