Revert "Support adding attributes to PDF document structure nodes."

This reverts commit 80474156d1100caba97430b631880b47e9a265ee.

Reason for revert: breaking chrome roll

https://ci.chromium.org/p/chromium/builders/try/cast_shell_linux/533554

Original change's description:
> Support adding attributes to PDF document structure nodes.
> 
> This is an important part of writing a tagged PDF. Many of the nodes
> in the document structure tree need additional attributes, just like
> in HTML.
> 
> This change aims to add support for a few useful attributes, not to
> be comprehensive.
> 
> Bug: chromium:1039816
> 
> Change-Id: I64a6b36b0b4ec42fd27ae4ad702afce95c95af5d
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268878
> Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
> Commit-Queue: Mike Reed <reed@google.com>
> Auto-Submit: Dominic Mazzoni <dmazzoni@chromium.org>
> Reviewed-by: Mike Reed <reed@google.com>
> Reviewed-by: Derek Sollenberger <djsollen@google.com>

TBR=djsollen@google.com,reed@google.com,dmazzoni@chromium.org,dmazzoni@google.com

Change-Id: Iedd397303e870144e8d282db0cb81c535a783e8b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1039816
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271858
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
6 files changed