[devtools/headless] Remove obsolete getLayoutTreeAndStyles command.

This (experimental) command is no longer used and was replaced by
DOMSnapshot.getSnapshot.

Bug: 546953
Change-Id: I8a0d3a0bf612d45c1ca99d9b819c14d063cdbf6c
Reviewed-on: https://chromium-review.googlesource.com/535696
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#479717}
11 files changed