ozone: remove x11 headers from accessibility tree formatter for Linux

That source file is platform agnostic and used by X11 and
Ozone/X11/Wayland. Remove unneseccary includes.

Test: compile test ozone/wayland only
Change-Id: I9d314988f1dff2ae16043619c947a068229de9f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216073
Auto-Submit: Maksim Sisov <msisov@igalia.com>
Commit-Queue: Martin Robinson <mrobinson@igalia.com>
Reviewed-by: Martin Robinson <mrobinson@igalia.com>
Cr-Commit-Position: refs/heads/master@{#771770}

content/browser/accessibility/accessibility_tree_formatter_auralinux.cc

@@ -21,8 +21,6 @@
 #include "content/browser/accessibility/accessibility_tree_formatter_utils_auralinux.h"
 #include "content/browser/accessibility/browser_accessibility_auralinux.h"
 #include "ui/accessibility/platform/ax_platform_node_auralinux.h"
-#include "ui/base/x/x11_util.h"
-#include "ui/gfx/x/x11.h"
 
 namespace content {