[A11y] Delete unused AXLayoutObject

No longer used after landing CL:5402730.

Bug: none
Change-Id: I920b662c53650c7a720bfc6395bdf69f2473810a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5407712


Commit-Queue: Mark Schillaci <mschillaci@google.com>
Reviewed-by: Mark Schillaci <mschillaci@google.com>
Auto-Submit: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280716}